n 


UNIVERSITY  OF  CALIFORNIA  Agricultural  Experiment  Station 

College  of  Agriculture  e.  w.  hilgard,  director 

BERKELEY,  CALIFORNIA 


CIRCULAR  No.  6. 

(Junk,  1903.) 


Methods  of  Physical  and  Chemical  Soil  Analysis. 

By  E.  W.  HILGARD. 

Revised  from  Bulletin  No.  38,  Bureau  of  Chemistry,  U.  S.  Department  of  Agriculture,  1893, 
and  reprinted  for  the  use  of  the  students  in  the  College  of  Agriculture. 


Before  entering  upon  the  details  of  physical  and  chemical  soil  investigation,  it  may 
not  be  superfluous  to  define  what  are  the  objects  to  be  accomplished  in  such  investiga- 
tions, both  from  the  standpoint  of  the  farmer  and  of  the  agricultural  expert. 

It  is  well  understood  that  in  the  present  state  of  knowledge,  the  chemical  analysis  of 
soils  long  cultivated  and  fertilized  affords,  alone,  but  a  limited  amount  of  information 
regarding  their  productiveness,  although  always  useful  in  defining  their  general  charac- 
ter and  obvious  deficiencies.  In  the  case  of  those  cultivated  without  fertilization,  even 
for  a  considerable  length  of  time,  chemical  analysis  will  afford  us  valuable  indications 
not  only  regarding  their  general  character,  but  also  in  respect  to  the  important  soil 
ingredients  most  likely  to  have  been  reduced  below  the  level  of  profitable  culture.  Yet, 
so  long  as  virgin  spots  fairly  representing  cultivated  lands  exist,  the  results  obtained 
by  the  examination  of  the  former  can  be  fruitfully  applied  to  the  latter. 

In  virgin  soils  the  indications,  as  experience  has  shown,  become  so  definite  as  to 
permit  a  close  forecasting  not  only  of  the  general  character  and  value  of  lands  not  yet 
brought  under  cultivation,  but  also  of  their  best  adaptations  and  of  the  probable  dura- 
tion of  productiveness  without  fertilization.  Chemical  analysis  can  thus,  when  com- 
bined with  the  physical,  geological,  and  botanical  examination  of  soils,  give  information 
of  such  direct  practical  importance,  that  in  the  newer  States  and  in  the  Territories  it 
becomes  a  reliable  guide  to  the  settler  in  the  choice  of  lands  and  cultures.  Such  work 
is  therefore  peculiarly  the  province  of  the  experiment  stations  west  of  the  Mississippi 
River. 

As  regards  physical  soil  analysis  as  practiced  in  Europe,  its  results  have  fallen  far 
short  of  the  expectations  which,  theoretically,  it  might  be  expected  to  fulfill,  viz.,  the 
definite  measurement  of  the  "tilling  qualities"  and  of  other  physical  coefficients  of 
soils.  The  judgment  regarding  these  points  deducible  from  the  great  majority  of 
mechanical  soil  analyses  as  usually  made  and  published,  affords  hardly  more  informa- 
tion than  could  be  derived  from  mere  hand  tests  on  the  dry  and  wet  soil.  Yet  it  is 
hardly  doubtful  that  a  proper  study  of  the  physical  composition  can  be  made  to  yield  a 
much  deeper  insight  into  the  functions  of  the  several  physical  soil  ingredients  and, 
consequently,  into  the  means  of  modifying  the  physical  properties  to  the  best  advantage. 

One  important  function  of  such  examinations  (about  the  feasibility  of  which  there 
can  be  no  reasonable  question)  is  the  identification  of  uncultivated  soils  with  those  of 
lands  already  under  cultivation,  thus  permitting  the  application  to  new  lands,  of 
experience  already  acquired.  But  in  order  to  attain  such  results,  not  only  must  the 
mode  of  sampling  in  the  field,  the  preparation  of  the  samples  for  analysis,  and  the 
physical  and  chemical  analysis  itself,  be  conducted  upon  a  well-considered  and  uniform 
system,  but  the  conditions  of  occurrence,  the  "lay,"  depth,  climate,  natural  vegetation, 


—    2    — 

etc.,  must  be  known  as  fully  as  possible,  since  all  tbese  factors  must  be  taken  into  con. 
sideration  in  interpreting,  for  practical  purposes,  the  results  of  the  physical  and  chemical 
examination.  Moreover,  in  determining  the  conditions  to  be  fulfilled  and  the  modus 
operandi,  all  arbitrary  conventions  should  be  avoided  as  much  as  possible,  since  all 
such  are  sure  to  be  violated,  sooner  or  later,  by  'workers  who  consider  themselves  as 
much  entitled  to  exercise  of  judgment  as  any  one  else.  In  developing  the  methods 
originally  suggested  by  D.  D.  Owen,  it  has  therefore  been  sought  to  establish  a  rational 
basis  inherent  in  the  nature  of  the  case,  as  far  as  possible,  and  to  determine  maxima  or 
minima  rather  than  arbitrarily  assumed  means.  The  detailed  motivation  of  all  these 
points  would  increase  this  report  far  beyond  the  admissible  limits;  but  references  are 
given  to  the  publications  in  which  such  points  are  discussed. 

For  brevity's  sake  a  detailed  description  of  the  manipulations  in  the  case  of  well- 
known  analytical  methods  is  omitted,  mentioning  only  some  critical  points  upon 
which  success  depends,  but  taking  for  granted  the  following  out  of  the  accepted  precepts. 

THE  SAMPLING  OF  SOILS. 

Since  the  practical  utility  of  soil  work  would  be  greatly  impaired  were  it  dependent 
only  upon  the  personal  exploration  of  the  wide  domain  by  the  experiment  station 
officers,  I  have  formulated,  and  long  used  successfully,  the  following  "Directions  for 
taking  Soil  Samples,"  that  are  forwarded  either  to  persons  desiring  information  as 
to  their  lands,  or  to  intelligent  farmers  residing  in  regions  of  which  the  soils  are  to  be 
investigated.     It  is  often  surprising  how  accurate  and  graphic  are  the  data  so  obtained. 

In  taking  soil  specimens  for  examination  the  following  directions  should  be  carefully 
observed,  always  bearing  in  mind  that  the  analysis  of  a  soil  is  a  long  and  tedious 
operation,  which  can  not  be  indefinitely  repeated: 

(1)  Do  not  take  samples  indiscriminately  from  any  locality  you  may  chance  to  be 
interested  in,  but  consider  what  are  the  two  or  three  chief  varieties  of  soil  which,  with 
their  intermixtures,  make  up  the  cultivable  area  of  your  region,  and  carefully  sample 
these  first  of  all;  then  sample  your  particular  soil  with  reference  to  these  typical  ones. 

(2)  As  a  rule,  and  whenever  possible,  take  specimens  from  spots  that  have  not  been 
cultivated,  nor  are  otherwise  likely  to  have  been  changed  from  their  original  condition 
of  "virgin  soils" — e.  g.,  not  from  ground  frequently  trodden  over,  such  as  roadsides, 
cattle  paths,  or  small  pastures,  squirrel  holes,  stumps,  or  even  at  the  foot  of  trees,  or 
spots  that  have  been  washed  by  rains  or  streams,  so  as  to  have  experienced  a  noticeable 
change,  and  not  to  be  a  fair  representative  of  their  kind. 

(3)  Observe  and  record  carefully  the  normal  vegetation,  trees,  herbs,  grass,  etc.,  of  the 
average  land ;  avoid  spots  showing  unusual  growth,  whether  in  kind  or  quality,  as  such 
are  likely  to  have  received  some  animal  manure  or  some  other  outside  addition. 

(4)  Always  take  specimens  from  more  than  one  spot  judged  to  be  a  fair  representative 
of  the  soil  intended  to  be  examined,  as  an  additional  guarantee  of  a  fair  average. 

(5)  After  selecting  a  proper  spot,  pull  up  the  plants  growing  on  it  and  brush  off  the 
surface  lightly  to  remove  half-decayed  vegetable  matter  not  forming  part  of  the  soil  as 
yet.  Dig  a  vertical  hole,  like  a  posthole,  at  least  20  inches  deep;  in  arid  regions,  not 
less  than  36  inches.  Scrape  the  sides  clean  so  as  to  see  at  what  depth  the  change  of  tint 
occurs  which  usually  marks  the  downward  limit  of  the  surface  soil,  and  record  it.  Take 
at  least  half  a  bushel  of  the  earth  above  this  limit,  and  on  a  cloth  (jute  bagging  should 
not  be  used  for  this  purpose,  as  its  fibers,  etc.,  become  intermixed  with  the  soil)  or 
paper,  break  it  up  and  mix  thoroughly,  and  put  up  at  least  a  pint  of  it  in  a  sack  or 
package  for  examination.  This  specimen  will,  ordinarily,  constitute  the  "soil." 
Should  the  change  of  color  occur  at  a  less  depth  than  6  inches  the  fact  should  be  noted, 
but  the  specimen  taken  to  that  depth  nevertheless,  since  it  is  the  least  to  which  rational 
culture  can  be  supposed  to  reach. 

In  case  the  difference  in  the  character  of  a  shallow  surface-soil  and  its  subsoil  should 
be  unusually  great— as  may  be  the  case  in  tule  or  other  alluvial  lands  or  in  rocky  dis- 
tricts— a  separate  example  of  that  surface  soil  should  be  taken,  besides  the  one  to  the 
depth  of  6  inches. 

(6)  Whatever  lies  beneath  the  line  of  change,  will  constitute  the  "subsoil."  But 
should  the  change  of  color  occur  at  a  greater  depth  than  12  inches  the  "soil "  specimen 


—  3  — 

should  nevertheless  be  taken  to  the  depth  of  12  inches  only,  which  is  the  limit  of  ordi- 
nary tillage;  then  another  specimen  from  that  depth  down  to  the  line  of  change,  and 
then  the  subsoil  specimens  beneath  that  line. 

The  depth  down  to  which  the  last  should  be  taken  will  depend  on  circumstances.  It 
is  always  necessary  to  know  what  constitutes  the  foundation  of  a  soil,  down  to  the 
depth  of  3  feet  at  least,  since  the  question  of  drainage,  resistance  to  drought,  etc.,  will 
depend  essentially  upon  the  nature  of  the  substratum.  But  in  ordinary  cases  in  the 
humid  region,  10  or  12  inches  of  subsoil  will  be  sufficient  for  the  purposes  of  examination 
in  the  laboratory.  The  specimen  should  be  taken  in  other  respects  precisely  like  that 
of  the  surface  soil,  while  that  of  the  material  underlying  this  "subsoil"  may  be  taken 
with  less  exactness,  perhaps  at  some  ditch  or  other  easily  accessible  point,  and  should 
not  be  broken  up  like  other  specimens,  so  as  to  preserve,  e.  g.,  the  character  of  "hard- 
pan  " 

In  the  arid  regions,  where  surface  soil  and  subsoil  are  very  much  less  definitely  differ- 
entiated, and  the  depth  of  the  soil  mass  is  usually  very  great,  it  is  in  most  cases 
advisable  to  take  samples  representing  the  average  of  each  foot,  from  the  surface 
down  to  4  or  5  feet ;  or  even  more,  according  to  circumstances. 

(7)  Specimens  of  salty  or  "  alkali "  soils  should,  when  practicable,  be  taken  toward 
the  end  of  the  dry  season,  when  they  will  contain  the  maximum  amount  of  the  injuri- 
ous ingredients  with  which  it  may  be  necessary  to  deal. 

Since  ordinarily  the  alkali  salts  are  contained  mainly  within  the  first  4  feet  below 
the  surface  within  which  the  salts  descend  or  rise  according  to  the  seasons,  it  will  for 
practical  purposes  mostly  be  sufficient  to  take  an  average  sample  of  a  4-foot  column, 
the  leaching  of  which  will  indicate  the  kind  and  amount  of  salts  to  be  dealt  with.  But 
the  last  portions  brought  up  by  the  soil  auger  should  at  least  be  cursorily  examined  for 
their  salt  content,  and  therefore  sent  separately.  In  some  cases  it  will  be  desirable  to 
sample  each  foot  of  the  column  separately. 

(8)  All  peculiarities  of  the  soil  and  subsoil,  their  behavior  in  wet  and  dry  seasons, 
their  location,  position— every  circumstance,  in  fact,  that  can  throw  any  light  on  their 
agricultural  qualities  or  peculiarities— should  be  carefully  noted  and  the  notes  sent 
with  the  specimens.  Unless  accompanied  by  such  notes,  specimens  can  not  ordinarily 
be  considered  as  justifying  the  amount  of  labor  involved  in  their  examination. 

It  will  be  noted  that  in  these  "  directions  "  the  depth  of  the  surface  "  soil "  sample  to 
be  taken  is  left  to  the  judgment  of  the  farmer,  between  the  limits  of  6  and  12  inches,  the 
first  being  the  minimum,  the  latter  the  maximum,  depth  to  which  rational  culture 
usually  reaches. 

When  the  soil  sample  is  to  be  transmitted  to  any  considerable  distance  it  is  very 
desirable  that  it  should  be  dried  in  the  sun  as  completely  as  possible  before  shipment, 
since  otherwise  not  only  does  it  often  arrive  in  an  abnormally  puddled  and  compacted 
condition,  but  may  become  moldy,  changing  the  natural  condition  not  only  of  the 
organic  but  also  of  the  reducible  inorganic  ingredients;  notably  that  of  ferric  hydrate 
and  nitrates.  With  respect  to  the  latter  the  date  of  taking  the  sample  is  also  desirable 
and  should  be  recorded  in  every  case. 

THE  MECHANICAL  OR  PHYSICAL  ANALYSIS  OF  SOILS. 

The  "insoluble  residue"  of  the  chemical  analysis  indicates  in  a  very  general  manner 
the  amount  of  "sand  "  in  a  soil ;  and  when  combined  with  a  determination  of  the  soluble 
silica,  alumina,  and  lime  we  also  gain  some  idea  of  possible  plasticity  or  "heaviness." 
But  these  indications  given  by  chemical  analysis  are  far  too  indefinite  for  practical 
requirements  It  is  to  the  mechanical  (or  physical)  analysis  that  we  must  look  for 
practically  available  data  on  the  tilling  qualities  of  soils;  but  the  loose  practice  mostly 
prevailing  thus  far  has  rendered  the  results  far  from  satisfactory. 

PRELIMINARY   EXAMINATION. 

The  first  step  toward  the  determination  of  the  character  of  a  soil  sample  should 
always  be  what  might  be  termed  the  hand  tests,  to  wit,  the  observation  of  the  greater  or 
jess  degree  of  ease  with  which  the  soil  lumps  crush  between  the  fingers  in  the  dry  con- 
dition ;  the  presence  or  absence  of  coarse  sand,  etc.;  also  the  change  of  color  on  wetting, 


_  4  — 

the  degree  of  rapidity  with  which  the  water  is  absorbed,  the  extent  to  which  it  softens 
the  lumps,  and  the  degree  of  plasticity  assumed  when  the  wet  soil  is  kneaded. 

The  next  step  should  be  the  at  least  approximate  identification  of  the  minerals  forming 
the  coarse  portion,  since  it  must  be  presumed  that,  as  a  rule,  these  represent  the  orig- 
inal nature  of  the  fine  grains  also.  We  thus  already  gain  a  very  close  insight  into  the 
origin  and  general  character  of  the  soil.  This  mineralogical  examination  is  advantage- 
ously combined  with  an  approximate  quantitative  determination  of  the  coarse  portion  by 
sedimentation  in  a  small  beaker,  or  more  advantageously,  by  means  of  a  "Kiihn's  cyl- 
inder" and  an  upward  current  of  water  of  definite  velocity  ;  that  of  2  mm.  per  second  is 
convenient  for  this  purpose,  provided  that  the  sample  is  kept  stirred  by  means  of  a  rod. 
The  dried  coarse  portion  is  weighed  and  then  examined  with  lens  and  microscope,  with 
or  without  previous  separation  by  means  of  Thoulet's  or  some  other  dense  fluid.  This 
examination  is  of  especial  value  in  the  identification  of  the  sample  with  other  soils 
previously  investigated,  and  thus  frequently  saves  a  very  large  amount  of  analytical 
labor. 

When  the  preliminary  examination  does  not  suffice  for  the  purposes  in  view,  and 
detailed  mechanical  or  "silt  analysis"  must  be  resorted  to,  more  elaborate  and  complex 
methods  and  appliances  are  called  for. 

SEDIMENTATION    AND    HYDRAULIC   ELUTRIATION. 

In  a  general  way  a  soil  may  be  considered  as  consisting  of  clay  intermixed  with  more 
or  less  mineral  powder  or  sand  of  various  grades  of  fineness,  together  with  some  humus 
or  vegetable  mold.  The  two  former  usually  determine,  in  the  main,  the  tilling  quali- 
ties of  the  soil. 

As  regards,  first,  the  conventional  "clay"  which  figures  in  the  analytical  statements, 
e.  g.,  of  the  German  investigators,  it  oftentimes  consists  far  more  of  fine  silex  than  even 
of  total  kaolinite  substance.  Since  the  latter  itself  consists  at  least  of  two  portions 
totally  distinct  in  their  physical  functions,  viz.,  of  chalky  crystalloid  grains  and  of  a 
"  colloidal,"  highly  diffusible,  and  extremely  adhesive  and  hygroscopic  portion,  the  pres- 
ence of  which  determines,  in  the  main,  the  corresponding  physical  properties  of  the 
soil,  the  indefiniteness  of  the  current  mode  of  statement  and  consequent  classification 
of  soils  is  so  great  as  to  render  a  clearer  and  more  rational  and  definite  method  of 
mechanical  analysis  absolutely  necessary  from  this  point  of  view  alone.  An  additional 
source  of  error  arises  from  the  viscosity  and  consequently  greater  hydraulic  efficacy  of 
''  clay  water,"  which  carries  off,  at  the  same  velocity,  much  larger  particles  of  rock  pow- 
der than  does  pure  water ;  or  in  the  case  of  subsidence,  permits  them  to  settle  much 
more  slowly.  The  consequence  is  that  the  percentage  of  a  sediment  of  a  given 
"  hydraulic  value  "  will  be  found  very  different,  according  to  the  amount  of  colloidal 
clay  present,  or  according  as  the  latter  has  or  has  not  been  wholly  or  partially  removed 
prior  to  the  separation  of  the  simply  pulverulent  or  sandy  ingredients.  Adding  to  these 
sources  of  uncertainty  the  wide  range  of  size  of  grain  included  and  weighed  as  one  sedi- 
ment by  most  observers,  the  slight  value  attaching  thus  far  to  the  results  of  mechanical 
soil  analysis  as  representing  the  farmer's  experience  is  amply  explained. 

For  the  separation  of  fine  powders  and  mixed  grain-sizes,  sedimentation  by  stirring 
up  in  water  and  drawing  off  the  suspended  sediment  with  the  water  after  a  definite 
time  allowed  for  the  subsidence  of  the  coarser  portions  is,  of  course,  the  simplest  process, 
which  has  been  used  in  the  arts  and  in  pharmacy  for  centuries.  For  analytical  purposes 
it  has  the  disadvantage  that  in  order  to  effect  a  reasonably  complete  exhaustion  of  a 
sediment  of  a  definite  size  or  "hydraulic  value,"  the  operation  of  stirring  up  and  drawing 
off  must  be  repeated  a  large  number  of  times,  since  the  time  of  subsidence  is  reckoned 
for  the  top  layer  of  water,  while  subsidence  actually  occurs  from  below  as  well.  The 
subsidence  method  requires  close  and  continuous  attention  in  its  execution  for  a  length 
of  time  proportioned  to  the  minuteness  of  subdivisions  desired ;  moreover,  in  the  case 
of  fine  sediments,  which  have  a  tendency  to  coalesce  (flocculate)  under  the  action  of  the 
irregular  currents  caused  by  stirring,  the  difficulty  of  obtaining  them  properly  segre- 
gated is  almost  insuperable,  greatly  detracting  from  the  accuracy  of  the  determinations. 
The  subsidence  or  (as  it  has  lately  been  termed)  "beaker"  method,  however  convenient 
on  account  of  its  simplicity,  is  therefore  ill  adapted  to  the  carrying  out  of  extended 
investigations  requiring  the  performance  of  a  large  number  of  mechanical  soil  analyses, 


—  5  — 

and  its  laboriousness  has  long  caused  it  to  be  replaced,  in  European  practice,  by  various 
devices  embodying,  in  a  more  or  less  perfect  form,  the  idea  of  separation  of  grain-sizes 
by  an  ascending  current  of  water,  or  "hydraulic  elutriation."  The  writer's  personal 
experience  has  brought  him  into  full  sympathy  with  this  view. 

When,  in  1872,  the  writer  began  the  consideration  of  this  subject  in  connection  with 
the  agricultural  survey  of  the  State  of  Mississippi,  even  a  very  superficial  test  led  him 
to  reject  quickly  the  grossly  inaccurate  and  misleading  apparatus  of  Nobel,  with  its 
four  vessels  of  ever-varying  capacity  and  form  and  inconstant  head  of  water.  The  best 
then  known,  that  of  Scheme,  proved  much  more  satisfactory,  provided  the  "colloidal 
clay"  was  first  removed.  But  even  then  there  remained  a  large  and  variable  residual 
error,  shown  in  the  mixed  grain-sizes  of  the  sediments  and  correspondingly  varying 
percentage  results.  A  protracted  investigation  of  the  causes  of  these  inaccuracies,  made 
in  the  years  1872  and  1873,  and  published  in  the  latter  year,*  proved  that  the  great  diffi- 
culty encountered  in  the  separation  of  soil  ingredients  by  the  ordinary  methods  of 
sedimentation  heretofore  employed  has  been  in  the  strong  tendency  of  the  fine  particles 
to  coalesce  into  large,  compound  floccules,  and  settle  with  the  coarser  sediments.  When 
violently  shaken  they  part  company  and  become  diffused  singly  through  the  liquid, 
which  then  presents  simply  a  general  turbidity;  the  particles  then  settling  down  slowly 
and  singly  at  the  rate  corresponding  to  their  individual  size  or  hydraulic  value. 

The  following  experiment,  well  suited  to  the  lecture  table,  serves  to  demonstrate  the 
above  principle:  If  a  given  quantity  of  pure  siliceous  sediment  of,  e.g.,  1  mm.  hydraulic 
value  (which  has  therefore  been  carried  off  at  the  velocity  of  1  mm.  by  an  ascending 
current  of  water)  be  again  placed  in  the  same  current,  in  a  long  conical  tube  with  cylin- 
drical outlet  above,  a  considerable  portion  will  fail  to  pass  off,  and  will  gather  into 
flocculent  aggregates,  revolving  in  the  lower  (narrow)  part  of  the  tube.  If  instead  of  the 
full  velocity  of  1  mm.  only  0.8  mm.  is  used,  none  of  the  sediment  will  pass  off,  but  after 
some  time  it  will  be  found  wholly  gathered  together  into  the  heavy  flocculent  aggregates, 
when  the  full  velocity  of  1  mm.  may  be  used  without  causing  any  considerable  portion 
of  sediment  to  be  carried  off,  until  by  violent  stirring  with  a  rod  the  floccules  are 
destroyed.  It  is  only,  however,  by  repeating  this  outside  stirring  a  number  of  times, 
that  it  is  possible  to  get  nearly  all  the  sediment  corresponding  to  the  velocity  of  current 
actually  used  to  pass  off,  The  stirring  by  the  current  itself  is  powerless  to  do  so,  because 
the  return  currents  down  the  sides  of  a  conical  tube  perpetually  cause  recoalescence  or 
"  flocculation." 

It  is  thus  clear  that  even  with  purely  siliceous  and  nongiutinous  sediments  correct 
results  can  not  be  obtained  so  long  as  conical  elutriator  tubes  are  employed;  and  this 
effectually  bars  the  claims  of,  e.  g.,  Schone's  apparatus  (now  adopted  by  the  German 
experiment  stations),  to  the  accuracy  desirable  in  this  work. 

But  if  cylindrical  elutriator  tubes  are  alone  admissible,  then  it  follows  that  agita- 
tion by  outside  power,  for  keeping  the  soil  or  powder  in  suspension  and  continuously 
resolving  the  floccules  inevitably  formed  under  the  circumstances,  is  indispensable. 
However,  the  tendency  to  coalescence  diminishes  of  course  as  the  size  of  the  grains 
increases,  but  does  not  altogether  cease  until  their  diameter  exceeds  0.2  mm.,  or  about 
16  mm .  hydraulic  value.  For  the  elutriation  of  coarser  sediments  hydraulic  stirring  may 
be  successfully  employed. 

We  may  therefore  formulate  as  follows  the  conditions  to  be  fulfilled  by  mechanical 
soil  analysis  upon  which  definite  conclusions  as  to  the  physical  and  agricultural  (or 
"working")  qualities  of  soils,  and  of  the  functions  of  the  several  grain-sizes  in  deter- 
mining the  same,  may  be  based  : 

(1)  The  preliminary  preparation  of  the  soil  sample  must  leave  its  natural  physical 
condition  unimpaired.  It  must,  therefore,  not  be  heated  to  any  temperature  likely  to 
wholly  or  partially  dehydrate  any  of  its  constituent  colloids  ;  nor  must  it  be  triturated 
or  "pestled"  in  any  manner  likely  to  destroy  the  naturally  existing  aggregates  or 
floccules  cemented  by  lime  carbonate,  ferruginous,  zeolithic,  or  other  cements;  nor 
must  the  latter  be  dissolved  by  the  use  of  acids,  thus  changing  the  natural  aggregates 
into  a  multitude  of  fine  particles  which  do  not  exist  in  the  original  soil,  and  perform 


*Amer.  Jour,  of  Sci.,  Oct.,  1873;   Proc.  Amer.  Assoc.  Adv.  Sci.,  Portland  meeting,  1873.    See  also 
The  Flocculation  of  Particles,"  Am.  J.  Sci.,  March,  1879. 


—  6  — 

the  physical  functions  of  sand  grains  of  corresponding  size.     Boiling  the  soil  is  free 
from  these  objections. 

(2)  Prior  to  any  attempt  to  separate  the  different  grain-sizes,  whether  by  the  hydraulic 
or  subsidence  method,  the  "colloidal  clay"  must  be  completely  removed ;  and  in  view 
of  the  prime  importance  of  the  latter  as  a  physical  soil  ingredient  it  must  be  deter- 
mined by  direct  weighing,  and  not  merely  by  loss,  or  "  difference  " 

(3)  If  the  hydraulic  method  be  used  for  the  separation  of  the  successive  grain-sizes 
this  must  be  done  in  vertical,  cylindrical  elutriator  tubes,  provided  with  a  device  for 
mechanical  stirring  by  outside  power,  for  preventing  and  undoing  the  flocculation  of 
the  sediments  into  heavy  aggregates  of  indefinite  composition  and  hydraulic  value. 

(4)  The  importance  of  discriminating  between  the  several  fine  sediments  in  respect 
to  their  physical  functions  is  so  great  that  a  much  larger  number  of  subdivisions  of 
these  must  be  made  than  is  now  usually  done.  This  proviso  renders  the  ordinary 
process  of  sedimentation  by  stirring  and  subsidence  in  cylindrical  vessels  (beaker 
method)  practically  inapplicable  to  any  extended  investigations  requiring  frequent  and 
numerous  mechanical  analyses,  since  each  one  would  take  an  amount  of  time  and 
practice  quite  out  of  reach  of  ordinary  laboratory  personnel.  The  work  must  in  the 
main  be  done  automatically  to  be  generally  available. 

The  ways  and  means  by  which  these  several  conditions  may  most  easily  be  fulfilled 
will  now  be  considered  in  detail. 

PRELIMINARY  PREPARATION. 

In  some  cases  simple  sifting  will  serve,  without  further  preparation,  to  separate  the 
original,  dry  soil  sample  into  appropriate  subdivisions,  down  to  the  fine  earth  that  is  to 
serve  for  detailed  mechanical  and  chemical  analysis.  In  most  cases,  however,  a  certain 
amount  of  mechanical  disintegration  must  be  resorted  to  in  order  to  detach  the  earth 
from  the  larger  sand  grains  and  aggregates,  and  here  some  judgment  must  be  exercised 
by  the  operator.  A  preliminary  washing,  aided  by  the  lens  and  microscope  if  neces- 
sary, will  show  whether  there  are  any  soft  concretions  or  decomposed  rock  particles 
likely  to  be  crushed  by  a  rubber  pestle,  the  hardest  material  admissible,  but  which  will 
serve  admirably  when  no  soft  grains  will  be  crushed  by  it,  thus  changing  the  nature  of 
the  soil  to  a  corresponding  extent.  The  liability  to  such  change  is  much  increased  by 
wetting  the  soil,  when  calcareous  and  ferruginous  concretions  (bog  ore)  may  be  crushed 
to  such  extent  as  to  destroy  the  value  of  the  work.  In  the  case  of  heavy  clay  ("adobe  ") 
soils,  however,  wetting,  and  even  hot  digestion  with  water,  may  be  necessary  to  even 
the  preliminary  disintegration  serving  to  prepare  a  fair  average  sample.  The  slushy 
mass  must  then  be  economically  washed  through  the  fine-earth  sieve  and  the  remnant 
afterwards  separated  into  sizes  by  sifting,  while  the  fine-earth  slush  is  evaporated  and 
dried  to  serve  for  analysis. 

Since  a  sieve  with  0.5  mm.  mesh  is  practically  about  the  finest  that  will  serve  for  the 
dry  separation  with  advantage,  and  since  that  same  diameter  is  almost  exactly  that  of 
quartz  grains  passing  off  at  the  maximum  current-velocity  conveniently  available,  viz., 
64  mm.  per  second,  the  writer  has  adopted  the  0.5  mm.  limit  as  practically  the  best  for 
the  fine  earth  to  be  used  for  both  mechanical  and  chemical  analysis.  It  is  to  such  fine 
earth  that  the  data  hereinafter  given  are  meant  to  apply. 

DISINTEGRATION   BY   BOILING. 

This  is  applicable  to  all  soils,  the  time  required  varying  greatly  with  different  ones. 
Those  containing  much  lime  carbonate  require  the  longest  time  to  resolve  those  aggre- 
gates which  will  be  also  destroyed  by  tillage.  Further  than  this  the  disintegration 
should  not  go ;  nor  should  it  fall  seriously  short  of  that  normal  measure.  Thirty  hours 
have  in  one  case  barely  sufficed  for  a  black  calcareous  prairie  soil,  while  three  have  been 
found  sufficient  to  reduce  other  soils  to  clean,  single  grains,  as  observed  under  the  lens. 
While  an  absolute  rule  can  not  therefore  be  given,  it  may  be  said  that  with  most  soils 
from  eight  to  fifteen  hours  will  be  the  right  measure,  which  with  some  may  extend  to 
twenty  and  twenty-four.  The  fact  ascertained  by  Osborne,  that  the  diff usibility  of  some 
clays,  at  least,  is  diminished  by  long  boiling,  renders  it  desirable  to  restrict  its  duration 
to  a  minimum. 


/>•* 


The  boiling  is  best  done  in  a  thin,  long-necked  copper  or  glass  flask  of  about  1  liter 
capacity,  tilled  four  fifths  full  of  distilled  water  and  laid  on  a  stand,  on  wire  netting,  at 
an  angle  of  40°  to  45°.  It  is  provided  with  a  cork  and  condensing  tube  of  sufficient 
length  (5  to  6  feet)  to  condense  all  or  most  of  the  steam  formed  when  ebullition  is  kept 
up  by  means  of  a  gas  flame.  For  a  few  hours  the  boiling  generally  proceeds  quietly; 
but  as  the  disintegration  progresses  violent  bumping  sets  in,  which  sometimes  endan- 
gers the  flask,  but  is  of  assistance  for  the  attainment  of  the  object  in  view.  In  extreme 
cases  some  of  the  heavier  sediment  (generally  clean  sand)  may  be  removed  from  the 
flask,  but  this  is  undesirable. 

It  is  frequently  the  case  that  when  the  boiled  contents  are  left  to  settle,  the  liquid 
appears  perfectly  clear  within  an  hour,  although  so  soon  as  they  are  largely  diluted  the 
clay  becomes  diffused  as  usual,  and  will  not  settle  in  weeks.  Probably  this  is  owing  to 
the  extraction  from  the  soil  of  soluble  salts,  which  exert  the  same  influence  as  does  lime 
or  common  salt,  even  in  very  dilute  solutions. 

REMOVAL   OF   THE   COLLOIDAL   CLAY   AND   FINEST  SEDIMENTS. 

The  boiled  fluid  with  sediment  is  transferred  to  a  beaker  and  diluted  so  as  to  form 
from  1  to  \%  liters  in  bulk,  and  being  stirred  up,  is  allowed  to  settle  for  such  a  length  of 
time  as  (taking  into  account  the  height  of  the  column)  will  allow  all  sediments  of  0.25 
mm.  hydraulic  value  to  subside,  the  process  being  repeated  with  smaller  quantities 
of  water  (distilled)  until  no  sensible  turbidity  remains  after  allowing  due  time  for 
subsidence. 

It  must  be  remembered  that  this  time  is  considerably  longer  than  that  for  pure 
water,  so  long  as  any  considerable  amount  of  clay  remains  in  the  liquid,  rendering  it 
more  viscous.  And  as  the  precise  amount  of  allowance  to  be  made  can  not  in  general  be 
foreseen,  some  sediment  of  and  exceeding  0.25  mm.  hydraulic  value,  will  almost  inevita- 
bly be  decanted  with  the  successive  clay  waters,  until  the  buoyant  effect  of  the  clay 
becomes  insensible.  The  united  clay  waters  (of  which  there  will  be  from  4  to  8  liters) 
must  therefore  be  again  stirred  up,  and  the  proper  time  allowed  for  the  sediments  of 
0.25  mm.  and  over  to  subside.  The  dilution  being  very  great,  a  pretty  accurate  separa- 
tion is  thus  accomplished ;  the  sediments  being  then  ready  for  the  elutriator. 

SEPARATION    OF   CLAY   AND   THE   FINEST   SILT   IN   THE   "CLAY   WATER." 

The  now  well-known  property  of  colloidal  clay,  of  remaining  suspended  in  pure 
water  for  weeks  and  even  months,  offers  an  obvious  method  of  separation  from  at  least 
the  greater  portion  of  silts  finer  than  0.25  mm.  hydraulic  value  «0.25).  To  push  this 
separation  to  the  extreme  of  attempting  to  remove  all  but  the  kaolinite  particles  proper, 
even  were  it  feasible,  would  carry  the  time  and  labor  required  for  the  determination 
beyond  the  limits  required  for  practical  purposes,  and  would  render  the  performance  of 
mechanical  analyses  rare  events  in  most  laboratories.  In  special  cases,  of  course,  it 
may  be  desirable  to  go  to  these  lengths,  and  also  to  divide  the  sediments  lying  between 
the  clay  proper  and  the  finest  sediment  that  can  conveniently  be  obtained  by  the 
hydraulic  method  (0.25  mm.  hydraulic  value)  into  two  or  more  groups,  when  it  is  very 
abundant. 

The  clay  water  for  subsidence  is  placed  in  a  wide  cylindrical  or  conical  vessel  (in 
which  it  may  conveniently  occupy  200  mm.  in  height);  it  is  there  allowed  to  settle  for 
twenty-four  hours.  This  interval  of  time  was  at  first  arbitrarily  chosen,  but  it  was 
subsequently  found  to  be  about  the  average  time  required  by  the  finest  siliceous  silt 
usually  present  in  soils,  to  sink  through  200  mm.  of  pure  water.  So  long  as  any  sensible 
amount  of  clay  is  present,  the  time  of  course  is  longer,  say  from  forty  to  sixty  hours,  or 
even  more,  if  the  clay  be  abundant  and  the  liquid  not  very  dilute.  The  sharp  line  of 
separation  between  the  dark  silt  cloud  below  and  the  translucent  clay  water  above  is 
readily  observed,  and  the  time  of  subsidence  regulated  accordingly.  At  times,  several 
such  lines  of  division  may  be  seen  simultaneously  in  the  column,  indicating  silts  of 
successive  sizes,  with  a  break  between.  No  such  appearance  is  presented  when,  after 
weeks  of  quiet,  the  clay  itself  gradually  settles.  The  liquid,  which  may  be  almost  clear 
at  the  surface,  then  shades  off  downward  very  gradually,  until  near  the  bottom  of  the 
vessel  it  becomes  entirely  opaque. 


—  8  — 

After  decantation  of  the  clay  water,  the  remaining  liquid  is  poured  off  temporarily, 
leaving  the  sediment  as  dry  as  possible.  It  is  then  rubbed  or  kneaded  in  the  decanting 
vessel  itself,  with  a  long-handled,  soft-rubber  pestle  (conveniently  cut  out  of  a  rubber 
cork).  At  this  point  the  addition  of  a  few  drops  of  ammonia  water,  according  to 
Schlosing's  prescription,  renders  good  service ;  but'  it  is  undesirable  to  use  any  large 
amount  of  ammonia,  as  it  impedes  the  subsequent  precipitation  of  the  colloidal  clay. 

Distilled  water  is  again  poured  on  (agitating  as  much  as  possible  to  break  up  the 
molecular  aggregates)  to  the  proper  height,  and  another  twenty-four  hours'  subsidence 
allowed.  This  operation  is  repeated  six  to  nine  times,  until  either  the  water  remains 
almost  clear  after  the  last  subsidence,  or  the  decanted  turbid  water  fails  to  be  precipi- 
tated by  salt  water,  showing  the  suspended  matter  to  be  pulverulent  silt  only. 

Doubtless  the  fine  silt  obtained  in  the  twenty-four  hours'  subsidence,  the  diameter  of 
whose  quartz  particles  varies  from  0.001  to  0.02  mm.,  is  not  entirely  free  from  adherent 
colloidal  clay,  as  is  indicated  by  its  deeper  tint,  compared  with  that  of  the  coarser 
sediments;  nor  is  the  "clay"  thus  obtained  free  from  the  finest  particles  of  quartz  and 
especially  of  ferric  oxid ;  but  it  is  doubtful  whether  for  practical  purposes  a  closer 
separation,  such  as  was  proposed  by  Williams,*  is  called  for. 

The  extent  to  which  these  contaminations  exist,  and  the  distribution  of  the  impor- 
tant soil  ingredients  among  the  several  sediments,  have  been  discussed  in  other  papers. 

Determination  of  the  Colloidal  Clay. — The  colloidal  portion  of  the  kaolinite  constitu- 
ent is  of  such  preeminent  importance  that  to  throw  upon  it  the  indefinite  "  loss  by 
analysis"  and  estimate  it  "  by  difference,"  is  hardly  excusable.  Two  ways  of  determin- 
ing it  directly  in  the  turbid  waters  from  the  twenty-four  hours'  subsidences  are  open  to 
us.  One  is  to  evaporate  the  whole  or  an  aliquot  portion ;  if  the  latter  is  not  too  small, 
and  the  soil  is  measurably  free  from  the  carbonates  of  lime  and  magnesia  and  other 
soluble  salts,  this  method  may  yield  fairly  satisfactory  results.  But  100  cc.  out  of  per- 
haps 20  liters  of  water,  as  has  been  practiced  by  some,  is  at  best  a  rather  minute  base 
line  to  go  upon  in  so  important  a  determination  ;  moreover,  it  is  so  desirable  to  have 
the  "clay  "  tangibly  before  one  for  examination,  that  we  consider  it  altogether  preferable 
either  to  evaporate  the  entire  amount  of  clay  water,  which  can  readily  be  done  pari 
passu  witn  the  sedimentation,  and  then  if  necessary  to  extract  the  soluble  portions  with 
water  or  very  dilute  acid.  I  consider  it  best,  however,  to  precipitate  the  clay  by  means 
of  a  saline  solution  and  thus  weigh  the  whole.  The  use  of  lime  water,  which  naturally 
suggests  itself,  is  so  complicated  by  chemical  reactions  and  other  elements  of  uncer- 
tainty, that  I  have  found  it  preferable  to  employ  simply  pure  rock-salt  brine  for  the 
precipitation.  Fifty  cc.  of  a  saturated  brine,  i.  e.,  1.5  per  cent  of  salt,  is  ordinarily 
sufficient  to  precipitate  1  liter  of  clay  water;  the  precipitation  is  much  favored  by 
warming.  Half  the  quantity,  or  even  less,  will  do  the  same,  but  more  time  is  required, 
and  the  precipitate  is  more  voluminous. 

In  practice  it  will  be  found  desirable  to  thus  precipitate  each  lot  of  clay  water  as 
soon  as  drawn  off.  The  clay  precipitate  (which  greatly  resembles  the  usual  iron- 
alumina  precipitate  of  chemical  analysis)  will  then  at  the  end  of  twenty-four  hours  have 
shrunk  into  so  small  a  bulk  that  on  drawing  off  the  supernatant  liquid,  the  succeeding 
clay  water  from  twenty-four  hours'  subsidence  may  be  mixed  with  it,  causing  it  to 
rediffuse;  the  same  being  done  at  each  succeeding  drawing  off.  This  mode  of  operation 
greatly  facilitates  and  shortens  the  gathering  of  the  colloidal  clay,  which  is  precipitated 
much  less  easily  and  sharply  from  very  dilute  waters  than  from  those  heavily  charged. 
As  the  clay  precipitate  can  not  ordinarily  be  washed  with  pure  water,  in  which  it 
quickly  diffuses,  it  must  be  collected  on  a  weighed  filter,  washed  with  a  weak  brine* 
dried  at  100°  and  weighed.  It  is  then  again  placed  in  a  funnel  and  washed  with  a  weak 
solution  of  sal  ammoniac,  until  the  chlorid  of  sodium  is  removed.  The  filtrate  is 
evaporated,  the  residue  ignited  and  weighed  ;  its  weight,  plus  that  of  the  filter,  deducted 
from  the  total  weight,  gives  that  of  the  clay  itself. 

In  some  cases,  especially  of  clays  and  subsoils  deeply  tinged  with  iron,  the  clay,  after 
drying  at  100°,  will  not  readily  diffuse  in  water,  and  can  be  washed  with  pure  water 
until  free  from  salt ;  it  can  then,  of  course,  be  weighed  directly. 


*  Wollny's  Forschungen  a.  d.  Gebiete  der  Agrikulturphysik,  vol.  18,  p.  225. 


IV 

—  9  — 

Properties  of  Pure  Clay.— The  "clay  "  so  obtained  is  quite  a  different  substance  from 
what  usually  comes  under  our  observation  as  such,  since  its  percentage  seems  rarely  to 
reach  75  in  the  purest  natural  clays,  40  to  47  in  the  heaviest  of  clay  soils,  and  8  to  20 
in  ordinary  loams.  Thin  crusts  of  it  are  occasionally  found  in  river  bottoms,  where 
clay  water  has,  after  an  overflow,  gradually  evaporated  in  undisturbed  pools.  When 
freshly  precipitated  by  salt  it  is  gelatinous,  resembling  a  mixed  precipitate  of  ferric 
oxid  and  alumina.  On  drying,  it  contracts  almost  as  extravagantly  as  the  latter,  crimp- 
ing up  the  filter,  to  which  it  tenaciously  clings,  and  from  which  it  can  be  separated 
only  by  moistening  on  the  outside,  when  it  may  mostly,  with  care,  be  peeled  off.  After 
drying  it  constitutes  a  hard,  often  horny,  mass,  difficult  to  break,  and  at  times  some- 
what resonant.  Since  the  ferric  oxid  with  which  the  soil  or  clay  may  have  been  colored 
is  mainly  accumulated  in  this  portion,  it  often  possesses  a  correspondingly  dark-brown 
or  chocolate  tint.  When  a  large  amount  of  iron  is  present  water  acts  rather  slowly  on 
the  dried  mass,  which  gradually  swells,  like  glue,  the  fragments  retaining  their  shape. 
Not  so  when  the  substance  is  comparatively  free  from  iron.  It  then  swells  up  instantly 
on  contact  with  water;  even  the  horny  scales  adhering  to  the  upper  portion  of  the  filter 
quickly  lose  their  shape,  bulge  like  a  piece  of  lime  in  process  of  slaking,  and  tumble 
down  into  the  middle  of  the  filter. 

There  is  a  marked  difference,  however,  in  the  behavior  to  water  of  clays  equally  free 
from  ferric  oxid,  some  exhibiting  the  phenomena  just  described  in  a  more  energetic 
manner  than  others.  On  the  whole,  those  freest  from  iron  appear  to  imbibe  the  water 
and  crumble  most  readily.  As  this  property  possesses  highly  important  bearings,  both 
on  the  agricultural  and  ceramic  qualities  of  clays,  we  propose  to  investigate  it  more 
minutely  hereafter. 

The  pure  clay,  when  dry,  adheres  to  the  tongue  so  tenaciously  as  to  render  its  sepa- 
ration painful.  When  moistened  and  worked  into  the  plastic  condition,  it  is  exceed- 
ingly tenacious  and  "  sticky,"  adhering  to  everything  it  touches. 

Under  a  magnifying  power  of  350  diameters  no  definite  particles  can  be  discovered 
in  the  opalescent  clay  water  remaining  after  several  weeks'  subsidence.  The  precipitate 
formed  by  saline  solutions  then  appears  as  an  indefinite  cloud  (mostly  of  a  yellowish 
tinge),  for  which  one  vainly  seeks  a  better  focus.  In  stronger  clay  water,  or  with 
higher  magnifying  powers,  one  can  discern  a  great  number  of  indefinite  punctiform 
bodies,  very  uniformly  diffused  throughout  the  liquid,  showing  active  "Brownian 
motion,"  and  apparently  opaque;  the  precipitate  then  formed  by  brine  also  shows  a 
faintly  dotted  structure  of  its  clouds.* 

Chemical  Nature  of  the  Clay  Precipitate. — While  usually  considered  as  consisting 
essentially  of  kaolinite  substance  in  a  state  of  extremely  fine  division,  the  colloidal  clay 
doubtless  contains  in  most,  if  not  in  all,  cases,  other  colloidals  or  "hydrogels,"  whose 
absorptive  functions  (albeit  not  plasticity)  are  in  a  measure  similar  to  those  of  clay. 
Since  in  many  cases  the  silica  set  free  by  treatment  of  the  precipitate  with  acid  is 
materially  below  that  of  the  alumina  dissolved  by  the  same  treatment,  it  follows  that 
free  aluminic  hydrate  is  then  present.  The  colloidal  ferric  hydrate,  likewise,  is  accu- 
mulated in  the  clay  precipitate,  and  so  are  amorphous  zeolitic  compounds.  While  it  is 
thus  certain  that  the  most  careful  mechanical  separation  of  this  clay  can  give  only  an 
approximation  to  the  really  plastic  kaolinite  substance,  yet  such  approximation  is 
infinitely  closer  than  that  attained  by  determination  of  total  alumina  by  boiling 
sulfuric  acid,  still  sometimes  prescribed  in  text-books.  As  in  such  treatment  all  the 
chalky  kaolinite  particles  are  also  decomposed,  it  does  not  lead  to  even  the  roughest 
approximate  estimate  of  the  soil's  plasticity. t  It  is  of  late  claimed  by  many  that  the 
latter  is  merely  a  function  of  extremely  fine  subdivision.  But  no  one  who  has  handled 
the  extremely  fine  portions  deposited  from  the  turbid  water  from  quartz  mills  in  the 
form  of  "  slickens  "  can  fail  to  appreciate  the  fact  that  even  though  these  quartz  pow- 
ders may  remain  in  suspension  as  long  as  the  clay  itself,  they  do  not  remotely  approach 
in  plasticity  even  to  an  ordinary  clay.  We  may  be  unable  to  define  the  physical  nature 
of  plasticity,  but  it  certainly  does  not  belong  as  such  to  all  fine  powders,  nor  to  other 
gelatinous  bodies. 

*  According  to  Williams  and  Whitney  the  finest  particles  of  colloidal  clay  are  0.0001  mm.  diame- 
ter. Wollny  gives  .001  mm.  as  the  limit,  stating  that  the  particles  have  the  form  of  short,  straight 
spicules.     Probably  the  subject  is  far  from  its  final  form  as  yet. 

t  See,  on  these  points,  my  article  on  "  The  determination  of  clay  in  soils."    Agr.  Science,  6, 156. 


—  11  — 

TREATMENT  OF  THE  COARSER  SEDIMENTS. 

The  mixed  sediments  remaining  after  the  separation  of  the  clay,  and  of  silts  of  less 
than  0.25  mm.  hydraulic  value  by  decantation,  are  ready  for  the  elutriator,  regarding 
which  some  general  conditions  have  already  been  given;  the  main  point  to  be  guarded 
being  the  prevention  of  the  formation  of  liocculent  aggregates  out  of  the  granules  of 
the  finer  sediments. 

The  Elutriator. — The  following  is  a  description  of  the  instrument  (see  plate)  as  devised 
by  me  for  the  purpose  of  breaking  up  these  flocculent  aggregates;  also  of  the  simpler 
form  (Schone's  elutriator  as  modified  by  me),  which  can  serve  for  grain-sizes  above 
8  mm.  hydraulic  value  (the  latter  is  conveniently  selected  as  to  have  half  the  cross- 
section  of  the  former,  so  that  with  the  same  position  of  the  index  lever  the  velocity  will 
be  just  doubled).  A  cylindrical  glass  tube,  of  about  45  mm.  inside  diameter  at  its 
mouth  and  290  to  300  mm.  high,  has  attached  to  its  base  a  rotary  churn,  consisting  of 
a  brass  cup,  shaped  like  an  egg  with  point  down,  so  as  to  slope  rather  steeply  at  base, 
and  triply  perforated,  viz..  at  the  bottom  for  connection  with  the  relay  reservoir;  at 
the  sides,  for  the  passage  of  a  horizontal  axis  bearing  four  grated  wings.  This  axis, 
of  course,  passes  through  stuffing  boxes  provided  with  good  thick  leather  washers, 
saturated  with  mutton  tallow.  These  washers,  if  the  axis  runs  true,  will  bear  many 
millions  of  evolutions  without  material  leakage  ;  when  a  beginning  is  noted  additional 
washers  may  be  slipped  on,  without  emptying  the  instrument,  until  the  analysis  is 
finished.  From  five  to  six  hundred  revolutions  per  minute  is  a  proper  velocity  for  the 
finest  sediments,  which  may  be  imparted  by  clockwork,  turbine,  or  electric  power.  The 
driving  pulley  should  not  be  directly  connected  with  the  axis,  both  because  this  is  liable 
to  cause  leakage,  and  because  it  is  necessary  to  be  able  to  handle  the  elutriator  quickly 
and  independently.  This  is  accomplished  by  the  use  of  "dogs"  on  the  pulley  and 
churn  axis.  For  the  grain-sizes  of  1  to  8  mm.  hydraulic  value,  lower  velocities  are 
sufficient.  Too  low  a  velocity  causes  an  indefinite  duration  of  the  operation,  and  may 
be  recognized  by  the  increase  of  turbidity  as  the  velocity  is  increased. 

As  the  whirling  agitation  caused  by  the  rotation  of  the  dasher  would  gradually  com- 
municate itself  to  the  whole  column  of  water  and  cause  irregularities,  a  wire  screen  of 
0.8  mm.  aperture  is  cemented  to  the  lower  base  of  the  cylinder. 

The  relay  vessel  below  the  churn  of  the  elutriator  tube  should  be  a  thick,  conical 
test  glass  with  foot.  Its  object  is  to  serve  as  a  reservoir  for  the  heavy  sediments  not 
concerned  at  the  velocity  used  in  the  elutriator  tube,  and  whose  presence  in  the  latter, 
or  in  its  base  (the  churn),  would  only  cause  abrasion  of  the  grains  and  changes  of  cur- 
rent velocity,  such  as  occur  in  the  apparatus  of  Schone,  and  compel  the  current  measure- 
ment of  the  water  delivered.  It  is  connected  above  with  the  churn  by  a  brass  tube 
about  10  mm.  in  clear  diameter,  so  as  to  facilitate  the  descent  of  the  superfluous  sedi- 
ments, which  the  operator,  knowing  the  proportion  of  area  between  the  connecting 
tube  and  elutriator,  can  carry  to  any  desired  extent,  thus  avoiding  the  disturbance  of 
the  gauged  current  velocities  as  well  as  all  material  abrasion. 

A  glass  delivery  tube  should  extend  quite  half  way  down  the  sides  of  the  relay  vessel 
to  insure  a  full  stirring  up  of  the  coarse  sediments  when  required.  By  means  of  a  rub- 
ber tube,  not  less  than  20  inches  in  length,  this  delivery  tube  connects  with  a  siphon 
carrying  the  water  from  near  the  bottom  of  a  Mariotte's  bottle— a  10-gallon  acid-carboy. 
A  stopcock,  provided  with  a  long,  stiff  index  lever  moving  on  an  empirically  graduated 
arc,  regulates  the  delivery  of  water  through  the  siphon.  Knowing  the  area  of  the  cross- 
section  of  the  elutriator  tube,  the  number  of  cubic  centimeters  of  water  which  should  pass 
through  it  in  one  minute  at  1  mm.  velocity  is  easily  calculated ;  and  from  this  the  lever 
positions  corresponding  to  other  velocities  are  quickly  determined  and  marked  on  the 
graduated  arc.  The  receiving  bottle  for  the  sediments  must  be  wide  and  tall,  so  as  to  allow 
the  sediment  to  settle  while  the  water  flows  from  the  top  into  the  waste  pipe.  The 
receiving  funnel  tube  must  dip  nearly  to  the  bottom  of  the  bottle. 

Thus  arranged  the  instrument  works  very  satisfactorily,  and  by  its  aid  soils  and  clays 
may  readily  be  separated  into  sediments  of  any  hydraulic  value  desired.  But  in  order 
to  insure  correct  and  concordant  results  it  is  necessary  to  observe  some  precautions, 
to  wit : 


—  12  — 

(1)  The  tube  of  the  instrument  must  be  as  nearly  cylindrical  as  possible,  and  must  be 
placed  and  maintained  in  a  truly  vertical  position.  A  very  slight  variation  from  the 
vertical  at  once  causes  the  formation  of  return  currents,  and  hence  of  fiocculent  aggre- 
gates on  the  lower  side. 

(2)  Sunshine,  or  the  proximity  of  any  other  source  of  heat,  must  be  carefully 
excluded.  The  currents  formed  when  the  instrument  is  exposed  to  sunshine  will  vitiate 
the  results. 

(3)  The  Mariotte's  bottle  should  be  frequently  cleansed,  and  the  water  used  be  as 
free  from  foreign  matters  as  possible.  For  ordinary  purposes  it  is  scarcely  necessary  to 
use  distilled  water.  The  quantities  used  are  so  large  as  to  render  it  difficult  to  main- 
tain an  adequate  supply,  and  the  errors  resulting  from  the  use  of  any  water  fit  for 
drinking  purposes  are  too  slight  to  be  perceptible,  so  long  as  no  considerable  devel' 
opment  of  the  animal  and  vegetable  germs  is  allowed.  Water  containing  the  slimy 
fibrils  of  fungoid  and  moss  prothalia,  algse,  vorticellse,  etc.,  will  not  only  cause  errors  by 
obstructing  the  stopcock  at  low  velocities,  but  these  organisms  will  cause  a  coalescence 
of  sediments  that  defies  any  ordinary  churning  and  completely  vitiates  the  operation. 

(4)  The  amount  of  sediment  discharged  at  any  one  time  must  not  exceed  that  pro- 
ducing a  moderate  turbidity.  Whenever  the  discharge  becomes  so  copious  as  to  render 
the  moving  column  opaque,  the  sediments  assume  a  mixed  character,  coarse  grains 
being  apparently  upborne  by  the  multitude  of  light  ones,  whose  hydraulic  value  lies 
considerably  below  the  velocity  used ;  while  the  churner  also  fails  to  resolve  the  molec- 
ular aggregates  which  must  be  perpetually  re-forming  where  contact  is  so  close  and 
frequent.  This  difficulty  is  especially  apt  to  occur  when  too  large  a  quantity  of  mate- 
rial has  been  used  for  analysis,  or  when  one  sediment  constitutes  an  unusually  large 
portion  of  it.  Within  certain  limits  the  smaller  the  quantity  employed  the  more  con- 
cordant are  the  results.  Between  15  and  20  grams  is  the  proper  amount  for  an  instrument 
of  the  dimensions  given  above. 

THE   FINE   SEDIMENTS  (0  25  TO   4  MM.  HYDRAULIC    VALUE). 

It  has  been  found  that,  practically,  0.25  mm.  per  second  is  about  the  lowest  velocity 
available  within  reasonable  limits  of  time,  and  that,  by  successively  doubling  the  veloci- 
ties up  to  64  mm.,  a  desirable  ascending  series  of  sediments  is  obtained,  provided 
always  that  a  proper  previous  preparation  has  been  given  to  the  soil  or  clay.  It  would 
seem  that,  according  to  the  prescription  given  above  for  the  preliminary  sedimentation, 
no  sediment  corresponding  to  0.25  mm.  velocity  should  remain  with  the  coarser  portion. 
That  such  is  nevertheless  always  the  case,  often  to  a  large  percentage,  emphasizes  the 
difficulty,  or  rather  impossibility,  of  entirely  preventing  or  dissolving  the  coalescence  of 
these  fine  grain-sizes  by  hand  stirring,  as  in  "beaker  elutriation."  It  is  only  by  such 
energetic  motion  as  is  above  prescribed  that  this  can  be  fully  accomplished,  and  the 
delivery  of  silts  of  0.25  and  0.50  mm.  hydraulic  value  really  exhausted. 

The  operation  is  best  begun  by  turning  on  a  low  velocity,  0.25  to  0.50  mm.,  and  then 
quickly  rinsing  the  sediments  from  a  small  beaker  into  the  elutriator  before  the  column 
reaches  the  top.  The  latter  is  then  quickly  closed  and  a  few  seconds'  subsidence  allowed 
with  diminishing  velocity,  so  that  the  turbid  column  shall  not  be  within  less  than 
30  mm.  of  the  top  when  the  velocity  desired  is  turned  on.  Otherwise  mixed  sediments 
may  pass  at  the  beginning.  At  first  the  sediment  passes  off  rapidly,  and  the  column 
remains  obviously  and  evenly  turbid  from  the  point  where  the  agitation  caused  by  the 
churner  ceases  to  the  top.  But  this  obvious  turbidity  generally  exhausts  itself  in  the 
course  of  a  few  hours,  and  it  then  requires  some  attention  to  determine  the  progress 
of  the  operation.  We  have  never  known  the  0.25  mm.  sediment  to  become  properly 
exhausted  in  less  than  fifteen  hours,  and  in  one  case  it  has  required  ninety.  The  more 
rigorously  the  process  of  preliminary  disintegration  above  described  has  been  carried 
out,  the  shorter  the  time  required  for  running  off  the  fine  sediments,  which  otherwise 
tax  the  operator's  patience  severely.  As  a  matter  of  fact  they  never  do  give  out  entirely, 
doubtless  for  the  reason  that  the  stirrer  continues  to  disintegrate  compound  particles 
which  had  resisted  the  boiling  process.  Besides,  downward  currents  on  the  sides  of  the 
vessel  will  form,  despite  all  precautions,  so  that  the  interior  surface  of  the  cylinder  some- 
times becomes  coated  with  Dendent  flakes  of  coalesced  sediment.    These  must  then 


t!>\ 


—  13  — 

from  time  to  time  be  removed  by  means  of  a  feather,  so  as  to  bring  them  again  under 
the  influence  of  the  stirrer;  but  it  is,  of  course,  almost  mathematically  impossible  that, 
under  these  circumstances,  any  of  the  sediments  subject  to  coalescence  should  ever 
become  completely  exhausted.  Practically,  the  degree  of  accuracy  attainable  at  best 
renders  it  unnecessary  to  continue  the  operation  beyond  the  point  when  only  a  milli- 
gram or  two  of  sediment  comes  over  with  each  liter  of  water.  It  is  admissible  and  even 
desirable  to  run  off  rapidly  the  upper  third  of  the  column  at  intervals  of  twenty  minutes, 
whereby  not  only  time  is  gained,  but  also  the  sediment  in  the  relay  reservoir  is  stirred 
and  brought  under  the  influence  of  the  churner  for  more  complete  disintegration. 

It  is  noticeable  that  recent  sediments,  river-alluvium,  etc.,  are  much  more  easily 
worked  than  more  ancient  ones;  as  might  be  expected.  Up  to  4  mm.  hydraulic  value 
the  use  of  the  rotary  stirrer  is  indispensable  on  account  of  the  tendency  to  the  forma- 
tion of  compound  particles.  Beyond,  this  tendency  measurably  disappears,  so  that  for 
the  coarse  sediments  of  8  to  64  mm.  hydraulic  stirring  may  be  employed  and  an  elutri- 
ating tube  of  smaller  diameter  may  advantageously  be  substituted  in  order  to  diminish 
the  otherwise  somewhat  extravagant  expenditure  of  water.  The  entire  amount  required 
for  one  analysis  is  from  25  to  30  gallons,  provided  a  thorough  previous  disintegration 
has  been  secured.  River  water  answers  in  ordinary  cases;  hard,  spring  or  well  waters 
are  undesirable.  Distilled  water  is  of  course  best,  and  by  a  simple  arrangement  of  an 
air-tight  reservoir  connected  with  a  pressure  chamber,  can  be  returned  to  the  Mariotte's 
bottle  and  used  over  and  over.  The  average  times  required  for  the  several  sediments 
are  as  follows : 

Sediment:  Hours. 

0.25  mm 30  to  40 

0.5  mm 15  to  25 

1.0  mm 5  to  10 

2  to  64  mm. 6  to  10 

Total 56  to  85 

With  proper  arrangements  much  of  this  can  be  done  automatically  at  night,  com- 
pleting an  analysis  (except  the  clay  and  finest  silt  determinations)  in  the  course  of 
three  or  four  days.  Of  course  only  a  very  small  portion  of  this  time  is  given  by  the 
operator  to  the  care  of  the  instrument.  He  can  carry  on  other  work,  just  as  when  an 
evaporation  is  going  on,  with  only  an  occasional  glance  to  see  that  the  water  supply 
holds  out  and  that  there  is  no  incipient  leakage  at  the  axis. 

As  the  soils  are  most  conveniently  weighed  "dried  at  100°,"*  the  sediments  should  be 
weighed  in  the  same  condition.  Great  care  is  necessary  to  obtain  the  correct  weight 
of  the  extremely  hygroscopic  clay.  The  same  is  true,  more  or  less,  of  the  <0.25  sedi- 
ment, which,  moreover,  is  so  diffusible  in  water  that  it  can  not  readily  be  collected  on  a 
filter.  It  is  best,  after  letting  it  subside  into  as  small  a  compass  as  possible,  to  evaporate 
the  last  25-50  cc.  in  the  platinum  dish  in  which  it  is  to  be  weighed.  From  the  other 
sediments  the  water  may  be  decanted  so  closely  as  to  render  their  determination  easy. 

The  loss  in  the  analysis  of  clays  and  subsoils  containing  but  little  organic  or  other 
soluble  matter  is  usually  from  1.5  to  2  per  cent,  resulting  partially,  no  doubt,  from  the 
loss  of  the  fine  silt  which  comes  off,  more  or  less,  throughout  the  process,  and  is 
decanted  with  the  voluminous  liquid.  When  the  turbidity  is  marked,  it  indicates 
imperfect  preliminary  disintegration;  it  may  be  removed,  and  the  silt  collected,  by 
adding  a  weighed  quantity  of  alum,  about  25  milligrams  per  liter,  precipitating  with 
ammonia,  and  deducting  from  the  weight  of  the  flocculent  precipitate  the  calculated 
amount  of  alumina. 

The  analysis  of  soils  very  rich  in  vegetable  matter  involves  some  modifications  in 
the  preliminary  treatment  and  final  weighings,  which  are  discussed  below.  Ignition 
of  the  soil  previous  to  elutriation,  as  proposed  by  some,  is  obviously  inadmissible,  as  it 
would  render  impossible  the  separation  of  the  clay  from  the  finer  sediments. 

As  heretofore  stated  (Am.  Jour.  Sci.,  Dec,  1872 ;  Proc.  Am.  Assoc.  Adv.  Sci.,  1872,  p.  71), 
the  writer  considers  that,  ordinarily,  the  investigation  of  the  subsoils  is  better  calculated 

*  A  somewhat  clayey  soil  will  continue  to  lose  weight  at  100°  for  five  or  six  days.  But  after  the 
first  six  hours  the  loss  becomes  insignificant  for  the  purpose  in  question. 


—  14  — 

to  furnish  reliable  indications  of  the  agricultural  peculiarities  of  extended  regions  than 
that  of  the  surface  soils,  which  are  much  more  liable  to  local  "freaks  and  accidents," 
and  usually  differ  from  the  corresponding  subsoils  in  about  the  same  general  points. 
For  practical  purposes,  therefore,  the  difficulties  incident  to  the  physical  analysis  of 
soils  rich  in  humus  may  in  most  cases  be  avoided.  ' 

Character  of  the  Sediments. — As  regards  the  size  of  the  particles  constituting  the  suc- 
cessive sediments,  the  most  convenient,  because  almost  universally  present,  material 
for  reference  is  quartz  sand.  Below  is  a  table  of  measurements  in  which  the  values 
given  refer  to  the  largest  and  most  nearly  round  quartz  grains  to  be  found  in  each  sedi- 
ment. As  a  matter  of  course,  all  sizes  between  that  given  and  the  one  next  below  are 
to  be  found  in  each  sediment.  A  few  grains  of  the  finer  sediments  are  also  invariably 
present,  owing  both  to  the  progressive  disintegration  of  agglomerated  particles  by 
the  stirrer,  and  to  the  inevitable  formation  of  the  flocculent  aggregates  of  the  finer 
sediments. 

While  the  measurement  of  the  quartz  grains  (which  are  rarely  wanting  in  a  soil 
or  clay)  affords  sufficient  landmarks  to  the  scientific  observer,  it  seems  desirable  to 
attach  to  them,  besides,  generally  intelligible  designations,  which  shall  approximately, 
at  least,  indicate  the  nature  of  the  sediment.  It  is  not  easy  to  indicate  in  popular  lan- 
guage distinctions  not  popularly  made,  but  the  grades  of  grain  indicated  in  the  common 
words,  grits,  sand,  and  silt,  may,  if  numerically  defined,  serve  at  least  to  establish  uni- 
formity of  expression  among  scientific  observers  and  reporters.  Thus  it  might  serve  a 
useful  purpose  to  apply  the  designation  of  "grits"  to  all  grains  above  1  mm.  diameter 
up  to  "gravel."  Below  1  mm.  down  to  0.1  mm.  might  be  "sand,"  all  below  that  "silt," 
viz. :  impalpable  powders.  Then  would  follow  clay,  of  which  the  distinctive  character 
is  not  only  impalpable  fineness  of  grain,  but  also  plasticity.  To  the  analyst,  however, 
the  designations  by  hydraulic  values  will  in  the  nature  of  the  case  always  remain  the 
most  convenient,  within  the  limits  of  the  use  of  either  sedimentation  or  hydraulic 
elutriation. 


Table  of  Diameters  and  Hydraulic  Values  of  Sediments. 


Designation  of  Materials. 


Diameter 

of  Quartz 

Grains. 


Velocity 
per  Second, 

or 

Hydraulic 

Value. 


mm. 

Grits :  1-3 

Grits .5-1 

Coarse  sand ._ ;  .50 

Medium  sand.. .30 

Fine  sand .16 

Fine  sand .12 

Coarse  silt  ... .072 

Coarse  silt .047 

Medium  silt .036 

Medium  silt .025 

Fine  silt ....  .016 

Fine  silt .010 

Clay (?) 


mm. 

(?) 

(?) 

64 

32 

16 

8 

4 

2 

1 

0.5 
0.25 
<0.25 
<0.0023 


It  is  noticeable  that  the  absolute  diameter  of  the  elutriator  tube  exerts  a  sensible 
influence  on  the  character  of  the  sediments,  in  consequence  of  comparatively  greater 
friction  against  the  sides  in  a  tube  of  small  diameter.  Strictly  speaking,  none  of  the 
sediments  actually  correspond  to  the  velocity  calculated  from  the  cross-section  of  the 
tube  and  the  water  delivered  in  a  given  time,  but  to  higher  ones,  whose  maximum  is  in 
the  axis  of  the  tube,  and  which  gradually  decrease  towards  the  sides,  according  to  a 


—  15  — 

law  which  may  be  demonstrated  to  the  eye  by  slightly  diminishing  the  velocity  while 
a  sediment  is  being  copiously  discharged,  so  that  the  turbid  column  remains  stationary 
while  clear  water  is  running  off.  The  surface  then  assumes  a  paraboloid  form,  which  is 
sensibly  more  convex  in  a  tube  of  smaller  diameter  than  in  a  wide  one;  the  results 
obtained  in  the  latter  being,  of  course,  nearest  the  truth. 

The  sediments  are  conveniently  preserved  in  homeopathic  vials  of  uniform  diameter; 
these,  when  arranged  in  a  row,  show  a  surface  curve  from  which  the  prominent  features 
of  the  physical  composition  of  a  soil  may  be  seen  at  a  glance. 

DETERMINATION   OF   THE   WATER  CAPACITY. 

This  determination  as  usually  made  is  very  indefinite  in  its  results,  varying, 
especially  in  pervious  soils,  according  to  the  height  of  the  soil  column  in  which  the 
water  is  absorbed.  This  is  due  to  the  obvious  fact  that  at  the  base  of  a  soil  column  there 
is  a  maximum  of  this  factor,  decreasing  regularly  towards  the  top  of  the  column,  where 
it  becomes  a  minimum.  Now  since  the  total  ascent  of  water  in  columns  of  different 
soils  varies  from  less  than  375  mm.  to  over  2,800  mm.,  it  is  clear  that  any  given 
uniform  height  of  column  arbitrarily  agreed  upon,  as  proposed  by  Ad.  Mayer  and 
others  (e.  g.,  60  or  200  mm.),  will  give  results  standing  in  no  direct  rational  relation  to 
the  maxima  and  minima  of  absorption  by  different  soils.  (See  Wollny's  Fortschr.  Agr. 
Physik,  15,  1.) 

It  is  evident  that  in  this  case,  as  in  others,  either  a  maximum  or  a  minimum  deter- 
mination, or  both,  should  be  agreed  upon  •  and  such  determination  should  be  made  in 
soil  columns  of  as  little  height  as  possible ;  that  is,  approaching  as  nearly  as  may  be  to 
the  theoretical  postulate  of  a  mere  differential.  I  suggest  as  the  lowest  practicable 
measure  for  this  purpose  a  column  of  10  mm.,  placed  in  a  circular  brass  box  with  per- 
forated bottom,  resembling  the  lead  sieve  of  Plattner's  blowpipe  chest,  and  containing 
exactly  25  or  50  cc.  In  this  both  the  maximum  and  minimum  absorption  is  determined 
for  each  soil,  proceeding  as  follows : 

Fill  the  box  full  of  air-dried  soil,  of  which  the  moisture  content  is  determined  in  a 
separate  portion  at  100°.  Settle  the  soil  by  a  gentle  tapping  of  the  box  on  a  table  and 
then  "  strike  "  it  level  as  in  measuring  grain  ;  weigh. 

Place  the  weighed  box,  plus  soil,  on  a  triangle  submerged  just  beneath  the  surface  of 
the  water  in  a  somewhat  wide  vessel;  allow  it  to  stand  until  fully  saturated  (not  less 
than  an  hour,  in  order  to  insure  the  complete  wetting  of  compacted  soil  particles);  then 
wipe  the  sieve  surface  rapidly  with  filter  paper  or  an  absorbent  towel  and  weigh  again 
without  unnecessary  delay.  Calculate  from  the  weighings  the  maximum  of  water  capac- 
ity with  respect  to  both  weight  and  volume.  Now  place  the  same  vessel  with  wet  soil 
on  a  flat  desiccator  plate,  and  immediately  cover  it  with  an  additional  (unweighed) 
quantity  of  the  same  soil,  in  order  to  absorb  all  the  water  down  to  the  minimum  of  liquid 
absorption. 

The  desiccator  plate,  as  well  as  the  bell  covering  it,  must  be  lined  with  wetted  blotting- 
paper  in  order  to  maintain  a  fully  saturated  atmosphere;  and  during  the  latter  portion 
of  the  process  of  minimization  at  least,  the  soil  used  must  itself  have  been  previously 
exposed  to  such  an  atmosphere  long  enough  to  fully  saturate  it  with  hygroscopic  moisture 
(see  below),  since  otherwise  such  moisture  would  be  taken  up  from  the  wetted  soil  and 
would  thus  vitiate  the  determination  of  liquid  water  capacity.  A  counterpoised  glass 
plate  on  the  scale  pan  of  the  balance  serves  to  cover  the  soil  cylinder  while  weighing. 

After  the  soil  above  has  become  imbued  with  moisture  it  is  cut  off  level  with  the 
edges  of  the  box  by  means  of  a  tense,  fine  silk  thread.  The  upper  portion  being  thrown 
off,  the  operation  is  repeated  until  the  fresh  quantities  of  soil  fail  to  become  moistened 
above  the  edge  of  the  box  and  cease  to  adhere,  and  weight  ceases  to  decrease  materially. 
Lastly,  blow  off  carefully  any  loose  particles  remaining  on  the  surface,  and  weigh.  Dry 
the  earth  in  the  box  thoroughly  at  100°  ;  weigh.  The  water  thus  driven  off  will  repre- 
sent the  minimum  of  liquid  absorption  plus  the  hygroscopic  moisture  originally  con- 
tained in  the  soil,  as  previously  determined  by  drying  at  100°.  The  soil  mass  will,  as  a 
rule,  be  found  somewhat  greater  than  that  calculated  from  the  first  determination, 
because  the  unavoidable  jarring  and  the  weight  of  the  soil  poured  on  the  wet  mass 
compacts  the  latter  to  some  extent. 


—  16  — 

By  simple  calculation  the  results  may  be  referred  to  either  of  the  two  quantities  for 
water  capacity  both  by  weight  and  volume,  allowing  for  the  increase  of  weight. 

It  is  clear  that  the  soil  so  depleted  of  the  water  held  in  liquid  absorption  down  to  the 
minimum  is  in  precisely  the  same  condition  as  a  similar  layer  of  soil  forming  the  top  of 
a  soil  column  in  which  the  water  has  been  allowed,  to  rise  to  its  maximum  height  by 
capillary  ascent.  It  seems  at  least  probable  that  hereafter  we  may  be  able  to  deduce 
from  these  determinations  the  absolute  height  to  which  water  will  rise  in  a  soil  column 
in  the  course  of  time;  but  thus  far  we  have  no  formula  for  such  a  deduction.  Wollny 
has  shown  (Forsch.  Agr.  Physik,  8,  197)  that,  as  a  general  rule,  the  differences  between 
the  maxima  and  minima  become  less  as  the  soil  becomes  more  fine-grained;  and  this 
difference  becomes  an  important  physical  datum  in  judging  of  the  capillary  efficiency 
of  the  soil.  We  can  then  by  the  above  method  attain  in  two  or  three  days  results  which 
by  direct  trial  would  require  at  least  as  many  months ;  and  the  differences  between  the 
maxima  and  minima  thus  ascertained  far  exceed  those  thus  far  on  record. 

METHOD   OF  CHEMICAL  SOIL  ANALYSIS. 

The  methods  of  chemical  soil  analysis  hereinafter  given  are  essentially  those  which 
in  their  main  features  have  been  pursued  by  Drs.  David  Dale  Owen  and  Robert  Peter 
in  the  work  of  the  geological  surveys  of  Kentucky  and  Arkansas,  and  which  have  since 
been  further  developed  by  the  writer  in  the  soil  work  of  the  surveys  of  Mississippi  and 
Louisiana;  in  that  done  in  connection  with  the  Tenth  Census  "Report  on  cotton 
culture"  throughout  the  cotton  States;  in  that  of  the  Transcontinental  Survey,  in  the 
States  of  Oregon,  Washington,  and  Montana  ;  and  in  the  soil  work  of  the  California 
experiment  station.  Altogether  these  methods  of  soil  investigation  have  been  applied 
to  over  a  thousand  virgin  soils,  the  analyses  of  which  are  strictly  comparable  among 
themselves;  therefore  by  far  the  largest  uniform  set  in  existence  thus  far.  Considering 
the  labor  involved  in  the  work  so  performed,  it  becomes  a  serious  question  whether 
there  are  any  valid  reasons  why  the  methods  employed  in  it  should  be  changed  in  any 
essential  points,  since  to  do  so  would  throw  out  of  any  possible  comparison  with  future 
work  the  bulk  of  what  has  heretofore  been  done  in  soil  investigation  on  the  North 
American  continent. 

It  is  for  this  reason  that  the  methods  are  given  in  considerable  detail,  not  with  a  view 
of  contesting  the  validity  or  equal  reliability  of  other  processes,  but  in  order  that  every 
possible  objection  may  now  be  raised,  before  more  work  shall  be  placed  in  jeopardy  of 
being  thrown  out  of  comparison  by  a  change  of  methods.  Their  convenience  and 
substantial  accuracy  within  the  limits  of  personal  error  having  been  tested  by  consider- 
able experience,  and  the  mode  of  interpreting  the  analytical  results  so  as  to  accord  with 
the  farmers'  experience  in  cultivation  having  been  developed  with  respect  to  analyses 
made  in  accordance  therewith,  there  should  be  strong  reasons  for  changing  the  methods 
before  such  action  is  finally  taken.  In  most  respects  the  course  of  analysis  here 
presented  does  not  differ  materially  from  that  laid  down  by  Kedzie  in  his  report  on  the 
same  subject;  the  chief  differences  arise  in  the  preliminary  operations,  but  are  there 
quite  vital,  so  as  to  necessitate  an  agreement  if  the  comparability  of  analyses  is  to  be 
maintained. 

It  should  be  understood  that  these  methods  contemplate  an  approximation  to  the  total 
maximum  of  solvent  effect  plants  can  exert  upon  the  soil;  carbonated  water  being  by  far  too 
feeble  as  a  solvent  to  represent  even  ordinary  plant  action,  while  hydrofluoric  acid  and 
fusion  with  alkalies  go  far  beyond  vegetative  possibilities.  It  is  certainly  desirable  that 
the  limit  of  extraction  should  be  a  natural  one  rather  than  an  arbitrary  convention, 
which  many  chemists  will  be  inclined  to  disregard  when  it  manifestly  does  not  fit  the 
case  before  them.  Experiments  have  shown  that  soils  extracted  with  strong  chlorhydric 
acid  are  permanently  *  sterile ;  and  if  it  can  be  shown  that  the  results  obtained  from 
such  soil  extraction  can  be  readily  correlated  with  the  permanent  agricultural  value  of 
soils,  the  most  important  postulate  of  soil  analysis  is  covered. 

PRELIMINARY   PREPARATION    OF   THE   SAMPLE. 

The  soil  is  thoroughly  broken  up,  dry,  with  a  rubber  pestle ;  or  in  the  case  of  clayey 
soils  is  digested  with  distilled  water  until  fully  disintegrated.    A  weighed  quantity 


i.  e  ,  within  the  time  interesting  to  the  living  generation. 


—  17  — 

(200  to  500  grams)  is  then  sifted  or  washed,  as  the  case  may  be,  through  a  sieve  of  0.5  mm. 
clear  aperture.  If  washed,  the  muddy  water  must  be  evaporated  to  dryness  with  the 
soil  slush  and  the  whole  thoroughly  mixed.  The  sample  so  obtained  constitutes  the 
"fine  earth"  to  be  used  in  chemical  analysis.  The  coarse  portions  are  to  be  further 
segregated  by  sieves,  weighed,  and  their  mineralogical  constituents  identified  with  the 
microscope,  reagents,  or  Thoulet's  solution,  as  the  case  may  require. 

That  the  introduction  of  the  grain-sizes  coarser  than  0.5  mm.  can  as  a  rule  serve  no 
useful  purpose  in  the  chemical  analysis  of  soils  in  the  humid  region  is  strikingly  shown 
in  the  investigation  made  by  R.  H.  Loughridge,  in  1873  (Am.  J.  Sci.,  Jan.  1874,  p.  17). 
He  found  that  in  the  case  of  a  very  generalized  soil  of  the  Mississippi  uplands,  solution 
by  strong  acid  practically  ceased  beyond  the  sediment  of  0.5  mm.  hydraulic  value,  cor- 
responding to  a  diameter  of  about  0.025  mm.  Although  the  general  applicability  of 
this  particular  limit  may  be  fairly  questioned,  the  wide  margins  between  the  fractions 
0.5  and  0.025  renders  it  pretty  certain  that  within  the  limit  of  the  former  we  shall  find 
all  that  is  of  any  value  to  plants  for  their  supply  of  mineral  plant  food.  But  for  the 
sake  of  comparability  with  analyses  made  under  a  different  rule,  the  grain-sizes  of 
0.5  to  1  and  1  to  2  mm,  diameter  should  always  be  quantitatively  determined. 

It  is  true  that  in  the  arid  region  the  larger  grains  contribute  to  plant  nutrition,  being 
themselves  covered  with  a  partially  decomposed  soil  material.  The  investigations  of 
Tolrnan*  have,  however,  shown  that  such  material  is  of  the  same  general  composition 
as  the  fine  earth.  If  it  be  desired  to  make  allowance  for  this  fact  by  including  the 
larger  grain-sizes,  it  would  be  necessary  to  employ  a  correspondingly  larger  amount  of 
soil  for  general  anatysis. 

DETERMINATION   OF   THE   HYGROSCOPIC   COEFFICIENT. 

The  fine  earth  is  exposed  to  an  atmosphere  saturated  with  moisture  for  about  twelve 
hours  at  the  ordinary  temperature  (p0°  P.)  of  the  cellar  in  which  the  box  should  be 
kept.  For  this  it  is  sifted  in  a  layer  of  about  1  mm.  thickness  upon  glazed  paper,  on  a 
wooden  table  in  a  small  water-tight  covered  box  (12  by  9  by  8  inches)  in  which  there  is 
about  an  inch  of  water;  the  interior  sides  and  cover  of  the  box  should  be  lined  with 
blotting  paper,  kept  saturated  with  water,  to  insure  the  saturation  of  the  air. 

"Air-dried  soil  "  yields  results  varying  from  day  to  day  to  the  extent  of  as  much  as 
30  to  50  per  cent,  nor  have  we  any  corrective  formula  that  would  reduce  such  observa- 
tions to  absolute  measure.  Knop's  law,  that  the  absorption  varies  directly  as  the  tem- 
perature, while  applicable  to  low  percentages  of  saturation,  is  wide  of  the  truth  when 
saturation  is  approached.  The  observation  of  the  writer  has  shown  that  between  the 
temperatures  of  about  7  and  23°  C.  the  coefficient  of  absorption  in  saturated  air  varies 
only  by  a  small  fraction ;  hence  the  ordinary  temperature  of  cellars  will  serve  well  in 
these  determinations  without  material  correction. 

After  eight  to  twelve  hours  the  earth  is  transferred  as  quickly  as  possible,  in  the 
cellar,  to  a  weighed  drying-bottle  and  weighed.  The  bottle  is  then  placed  in  an  air 
bath,  the  temperature  of  which  is  gradually  raised  to  110°  C.  and  kept  so  for  one  hour.  It 
is  then  weighed  and  the  drying  repeated  until  a  practically  constant  weight  is  obtained. 
The  loss  in  weight  gives  the  hygroscopic  moisture  in  saturated  air. 

GENERAL   ANALYSIS. 

The  samples  for  general  analysis  and  phosphoric  acid  determination  are  weighed  out 
from  the  air-dried  sample  in  which  the  hygroscopic  moisture  is  afterward  determined. 

In  determining  the  amount  of  material  to  be  employed  for  the  general  analysis 
regard  must  be  had  to  the  nature  of  the  soil.  This  is  necessary  because  of  the  impracti- 
cability of  handling  successfully  such  large  precipitates  of  alumina  as  would  result 
from  the  employment  of  even  as  much  as  5  grams  in  the  case  of  calcareous  clay  soils ; 
while  in  the  case  of  very  sandy  soils  even  that  quantity  might  require  to  be  doubled  in 
order  to  obtain  weighable  amounts  of  certain  ingredients.  For  average  loam  soils  in 
which  the  insoluble  portion  ranges  from  60  to  80  per  cent,  2.5  to  3  grams  is  about  the 
right  measure  for  general  analysis,  while  for  the  phosphoric  acid  determination  not  less 
than  3  grams  should  be  employed  in  any  case.    It  has  been  alleged  that  larger  quanti- 

*  Report  of  the  California  Experiment  Station  for  1899-1900,  page  33. 


—  18  — 

ties  must  be  taken  for  analysis  in  order  to  secure  average  results.  It  is  difficult  to  see 
why  this  should  be  true  for  the  fine  earth  of  soils  and  not  for  ores,  in  which  the  results 
affect  directly  the  money  value;  while  in  the  case  of  soils  the  interpretation  of  results 
allows  much  wider  limits  in  the  percentages.  Correct  sampling  must  be  presupposed  to 
make  any  analysis  useful ;  but  with  modern  balances  and  methods  it  is  difficult  to  see 
why  5  grams  should  be  employed  instead  of  half  that  amount,  which  in  some  cases  is 
still  too  much  for  convenient  manipulation  of  certain  precipitates  unless  parting  into 
aliquot  portion  is  resorted  to;  which  in  the  case  of  the  iron-alumina  precipitation 
would  be  very  desirable,  but  can  not  usefully  be  carried  out  in  practice.  It  is  very  much 
more  difficult  to  secure  a  correct  average  sample  when  the  coarser  sizes  of  sand,  such  as 
1-2  mm.  diameter,  are  retained  in  the  fine  earth,  as  these  tend  to  settle  down  out  of  the 
finer  portions.  If,  then,  these  larger  sizes  are  insisted  upon,  10  or  more  grams  must  be 
employed  in  order  to  secure  a  fair  average  sample. 

(1)  The  weighed  quantity,  usually  of  2  to  2.5  grams,  is  brought  into  a  small  porcelain 
beaker  covered  with  a  watch  glass,  treated  with  8  to  10  times  its  bulk  of  hydrochloric 
acid  of  1.115  sp.  gr.  and  2  or  3  drops  of  nitric  acid,  and  digested  for  five  days  over  the 
laboratory  steam  bath.  At  the  end  of  this  time  it  is  evaporated  to  dryness,  first  on  the 
water  bath  and  then  on  the  sand  bath.  By  this  treatment  all  the  silica  set  free  is 
rendered  insoluble. 

In  an  investigation  made  by  Loughridge  in  1873  (Am.  J.  Sci.,  Jan.,  1874,  p.  20)  it 
was  found  that  acid  of  the  above  strength  exerted  a  higher  solvent  power  than  that 
materially  stronger  or  weaker  (1.100  or  1.160  sp.  gr.).  He  also  found  that  after  the  fifth 
day  no  further  essential  solvent  action  occurred.  The  above  standard  strength  is  easily 
prepared  by  steam  distillation  of  acid  either  stronger  or  weaker.  Later  investiga- 
tions by  Jaffa  show  that  the  effect  of  such  acid  approximates  closely  to  that  of  oxalic 
acid,  the  strongest  solvent  available  for  plant-root  action.  We  therefore  determine  in 
such  treatment  the  maximum  effect  vegetation  can  exert  on  soils. 

The  evaporation  residue  is  now  moistened  with  strong  hydrochloric  acid  and  2  or  3 
drops  of  nitric  acid,  warmed,  and,  after  allowing  it  to  stand  a  few  hours  on  the  water 
bath,  treated  with  distilled  water.  After  clearing  it  is  filtered  from  the  insoluble  residue, 
which  is  strongly  ignited  and  weighed.  If  the  filtrate  should  be  turbid  the  insoluble 
residue  which  has  gone  through  the  filter  can  be  recovered  in  the  iron-and-alumina 
determination. 

The  insoluble  residue  is  next  boiled  for  fifteen  or  twenty  minutes  in  a  concentrated 
solution  of  carbonate  of  soda,  to  which  a  few  drops  of  caustic  lye  should  then  be  added, 
to  prevent  reprecipitation  of  the  dissolved  silica.  The  solution  must  be  filtered  hot. 
The  difference  between  the  weight  of  the  total  residue  and  that  of  undissolved  sand  and 
mineral  powder  is  recorded  as  soluble  silica,  being  the  aggregate  of  that  set  free  by  the 
acid  treatment  and  that  previously  existing  in  the  soil.  The  latter,  however,  rarely 
reaches  0.5  per  cent. 

(2)  The  acid  filtrate  from  the  total  insoluble  residue  is  evaporated  to  a  convenient 
bulk.  In  case  the  filtrate  should  indicate  by  its  color  the  presence  of  any  organic 
matter,  it  should  be  oxidized  by  aqua  regia,  otherwise  there  will  be  difficulty  in  separat- 
ing alumina. 

(3)  The  filtrate  thus  prepared  is  now  brought  to  boiling  and  treated  sparingly  with 
ammonia,  whereby  iron  and  alumina  are  precipitated.  It  is  kept  boiling  until  the 
excess  of  ammonia  is  driven  off,  and  then  filtered  hot  (Mitscherlich  method).  (Filtrate 
A.)  The  previous  addition  of  ammonic  chlorid  is  usually  unnecessary.  If  the  boiling 
is  continued  too  long,  filtration  becomes  very  difficult,  and  a  part  of  the  precipitate 
may  redissolve  in  washing.  Filtration  may  be  begun  so  soon  as  the  nose  fails  to  note 
the  presence  of  free  ammonia;  test  paper  is  too  delicate.  Failure  to  boil  long  enough, 
or  permitting  the  precipitated  solution  to  cool,  involves  the  contamination  of  the  iron- 
alumina  precipitate  with  lime  and  manganese. 

(4)  The  iron  and  alumina  precipitate  (with  filter)  of  No.  3  is  dissolved  in  a  mixture 
of  about  5  cc.  hydrochloric  acid  and  20  cc.  water.  Then  filter  and  make  up  to  150  cc. 
Take  50  cc.  for  the  determination  of  iron  and  alumina  together  by  precipitation  with 
ammonia,  after  oxidizing  the  organic  matter  (filter)  with  aqua  regia;  also  50  cc.  for 
iron  alone ;  keep  50  cc.  in  reserve.  Determine  the  iron  by  means  of  a  standard  solution 
of  permanganate  of  potash  after  reduction  ;  this  latter  is  done  by  evaporating  the  50  cc. 


—  19   - 

almost  to  dryness  with  strong  sulfuric  acid,  adding  water  and  transferring  the  solu- 
tion to  a  flask,  and  then  reducing  by  means  of  pure  metallic  zinc  in  the  usual  way. 
The  alumina  is  then  determined  by  difference.  This  method  of  determining  the  two 
oxids  in  their  intermixture  is  in  several  respects  more  satisfactory  than  the  separation 
with  alkaline  lye,  which,  however,  has  served  for  most  determinations  made  until 
within  the  last  twenty  years.  It  is  much  more  liable  to  miscarry  in  unpracticed  hands 
than  the  other. 

(5)  The  filtrate  A.  from  iron  and  alumina  is  acidified  slightly  with  HC1,  and  if  too 
bulky  is  evaporated  down  to  about  25  cc.  (unless  the  soil  is  a  very  calcareous  one)  and 
the  lime  precipitated  from  it  by  neutralizing  with  ammonia  and  adding  amnionic 
oxalate.  The  precipitation  of  the  lime  should  be  done  in  the  hot  solution,  as  the  pre- 
cipitate settles  much  more  easily.  It  is  allowed  to  stand  for  twelve  hours,  then  filtered 
off,  washed  with  cold  water,  and  dried  (filtrate  B ).  By  ignition  the  lime  precipitate  is  par- 
tially converted  into  the  oxid.  It  is  then  heated  with  excess  of  powdered  ammonium 
carbonate,  moistened  with  water,  and  exposed  to  a  gentle  heat  (50°-80°  C.)  until  all  the 
ammonia  is  expelled.  It  is  then  dried  below  red  heat  and  weighed  as  lime  carbonate. 
When  the  amount  of  lime  is  at  all  considerable,  the  treatment  with  ammonic  carbonate 
must  be  repeated  until  a  constant  weight  is  obtained. 

(6)  The  filtrate  B  from  the  calcic  oxalate  is  put  into  a  hard  Bohemian  or  Jena  flask, 
boiled  down  over  the  sand  bath  and  the  ammoniacal  salts  destroyed  with  aqua  regia 
(Lawrence  Smith's  method).  From  the  flask  it  is  removed  to  a  small  beaker  and  evapo- 
rated to  dryness  with  excess  of  HN03.  This  process  usually  occupies  four  to  five  hours. 
The  residue  should  be  crystalline-granular;  if  white-opaque,  ammonic  nitrate  remains 
and  must  be  destroyed  by  HC1. 

The  dry  residue  is  now  moistened  with  nitric  acid  and  the  floccules  of  silica  usually 
present  separated  by  filtration  from  the  filtrate,  which  should  not  amount  to  more  than 
10  or  15  cc.  Sulfuric  acid  is  then  precipitated  by  treatment  with  a  few  drops  of  baric 
nitrate,  both  the  solution  and  the  reagent  being  heated  to  boiling.  If  the  quantity  of 
S03  is  large,  it  may  be  filtered  off  after  the  lapse  of  four  or  five  hours.  If  very  small, 
let  it  stand  twelve  hours.  The  precipitate  is  washed  out  with  boiling  water,  dried, 
ignited,  and  weighed  (filtrate  C).  Care  should  be  taken  in  adding  the  barium  nitrate  to 
use  only  the  least  possible  excess,  because  in  such  a  small  concentrated  acid  solution  the 
excess  of  barium  nitrate  may  crystallize  and  will  not  readily  dissolve  in  hot  water. 
Care  must  also  be  taken  not  to  leave  in  the  beaker  the  large  heavy  crystals  of  baric 
sulfate,  a  few  of  which  sometimes  constitute  the  entire  precipitate,  rarely  exceeding  a 
few  milligrams.  Should  the  ignited  precipitate  show  an  alkaline  reaction  on  moisten- 
ing with  water,  it  must  be  treated  with  a  drop  of  HC1,  refiltered  and  weighed.  The  use 
of  barium  acetate  involves  unnecessary  trouble  in  this  determination. 

(7)  Filtrate  C  from  S03  precipitate  is  now  evaporated  to  dryness  in  a  platinum  dish; 
the  residue  is  treated  with  an  excess  of  crystallized  oxalic  acid,  moistened  with 
water,  and  exposed  to  gentle  heat.  It  is  then  ignited  to  change  the  oxalates  to  car- 
bonates. This  treatment  with  oxalic  acid  must  be  made  in  a  vessel  which  can  be  kept 
well  covered  with  a  thin  watch  glass,  otherwise  there  is  danger  of  loss  through  spattering. 
As  little  water  as  possible  should  be  used,  as  otherwise  loss  from  evolution  of  carbonic 
gas  is  difficult  to  avoid.  Spatters  on  the  cover  should  not  be  washed  back  into  the  basin 
until  after  the  excess  of  oxalic  acid  has  been  volatilized.  The  ignited  mass  should  have 
a  slightly  blackish  tinge  to  prove  the  conversion  of  the  nitrates  into  carbonates.  White 
portions  may  be  locally  retreated  with  oxalic  acid.  The  ignited  mass  is  treated  with  a 
small  amount  of  water,  which  dissolves  the  alkali  carbonates  and  leaves  the  carbonates 
of  magnesia,  protosesquioxid  of  manganese,  and  the  excess  of  barium  carbonate  behind. 
The  alkalies  are  separated  by  filtration  into  a  small  platinum  dish  (filtrate  D),  and  the 
residue  is  well  but  economically  washed  with  water  on  a  small  filter.  When  the  filtrate 
exceeds  10  cc,  it  may  on  evaporation  show  so  much  turbidity  from  dissolved  earthy 
carbonates  as  to  render  refiltration  on  a  minute  filter  necessary,  since  otherwise  the 
soda  percentage  will  be  found  too  large,  magnesia  too  small.  If  on  dissolving  the 
ignited  mass  the  solution  should  appear  greenish  from  the  formation  of  alkaline  man- 
ganates,  add  a  few  drops  of  alcohol  to  reduce  the  manganese  to  insoluble  dioxid.  The 
residue  of  barium,  magnesium,  and  manganese  compounds  is  treated  on  the  filter  with 
hydrochloric  acid,  and  the  platinum  dish  is  washed  with  warm  nitric  acid  (not  hydro- 


—  20  — 

chloric,  for  the  platinum  dish  may  be  attacked  by  chlorin  from  the  manganese  oxid), 
dissolving  any  small  traces  of  precipitate  that  may  have  been  left  behind. 

(8)  The  solution  containing  the  chlorids  of  magnesium  and  manganese  is  freed  from 
the  barium  salts  by  hot  precipitation  with  sulfuric  acid,  and  the  barium  sulfate 
after  settling  a  few  hours  is  filtered  off.  The  filtrate  is  neutralized  with  ammonia,  any 
resulting  small  precipitate  (of  iron)  is  filtered  off,  and  the  manganese  precipitated  with 
bromine  water.  Let  stand  twelve  hours  (or  over  night)  and  filter  (filtrate  E);  wash 
with  cold  water,  dry,  ignite,  and  weigh  as  manganese  protosesquioxid  Mn304. 

(9)  From  the  filtrate  E  (from  the  manganese),  the  magnesia  is  precipitated  by  adding 
an  equal  bulk  of  ammonia  water  and  then  sodic  phosphate.  After  standing  at  least 
twenty-four  hours,  the  magnesia  salt  may  be  filtered  off,  washed  out  with  ammoniacal 
water,  dried,  ignited,  and  weighed  as  magnesium  pyrophosphate. 

(10)  The  filtrate  E,  which  should  not  be  more  than  10  or  15  cc,  containing  the  car- 
bonates of  the  alkalies,  is  evaporated  to  dryness  and  gently  fused,  so  as  to  render 
insoluble  any  magnesium  carbonate  that  may  have  gone  through ;  then  redissolved 
and  filtered  into  a  small  weighed  platinum  dish  containing  a  few  drops  of  dilute 
hydrochloric  acid,  to  change  the  carbonates  into  chlorids ;  evaporated  to  dryness) 
exposed  to  a  gradually  rising  temperature  (below  red  heat),  by  which  the  chlorids  are 
thoroughly  dried  and  freed  from  moisture,  so  as  to  prevent  the  decrepitation  that  would 
otherwise  occur  on  ignition.  Then,  holding  the  platinum  basin  firmly  by  forceps 
grasping  the  clean  edge,  pass  it  carefully  over  a  very  low  Bunsen  flame,  so  as  to  cause, 
successively,  every  portion  of  the  scaly  or  powdery  residue  to  collapse,  without  fully 
fusing.  There  is  thus  no  loss  from  volatilization,  and  no  difficulty  in  obtaining  an 
accurate,  constant  weight.  The  weighed  chlorids  are  washed  by  means  of  a  little  water 
into  a  small  beaker  or  porcelain  dish,  treated  with  a  sufficient  quantity  of  platinic 
chlorid,  and  evaporated  to  dryness  over  the  water  bath.  The  dried  residue  is  treated 
with  a  mixture  of  3  parts  absolute  alcohol  and  1  part  ether,  leaving  the  potassio-platinic 
chlorid  undissolved.  This  is  put  on  a  filter,  and  washed  with  ether-alcohol.  When 
dried,  the  precipitate  and  filter  are  put  into  a  small  platinum  crucible  and  exposed  to  a 
heat  sufficiently  intense  to  reduce  the  platinum  chlorid  to  metallic  platinum  and  to 
volatilize  the  greater  part  of  the  potassium  chlorid.  This  is  easily  accomplished  in  a 
small  crucible,  which  is  roughened  by  being  constantly  used  for  the  same  purpose  (and 
no  other),  the  spongy  metal  causing  a  ready  evolution  of  the  gases.  (See  Fres.  Ztschr. 
anal.  Chem.,  1893.)  The  reduced  platinum,  which  should  adhere  firmly  to  the  crucible 
after  ignition  over  a  blast  lamp  for  twenty  minutes,  is  now  first  washed  in  the  crucible 
with  hot  acidulated  water,  then  with  pure  water;  then  all  moisture  is  driven  off  and  it 
is  weighed.  From  the  weight  of  the  platinum  is  calculated  the  potassic  chlorid  and 
the  oxid  corresponding;  the  difference  between  the  weights  of  the  total  alkali  chlorids 
and  potassic  chlorid  gives  the  sodic  chlorid,  from  which  may  be  calculated  the  sodic 
oxid.  When  the  heating  of  the  platinum  precipitate  has  not  been  sufficient  in  time  or 
intensity,  instead  of  being  in  a  solid  spongy  mass  of  the  color  of  the  crucible  itself, 
small  black  particles  of  metallic  platinum  will  obstinately  float  on  the  surface  of  the 
water  in  the  crucible,  and  it  becomes  difficult  to  wash  by  decantation  without  loss. 

PHOSPHORIC  ACID  DETERMINATION. 

(11)  The  weighed  quantity  (usually  of  3  to  5  grams)  is  ignited  in  a  platinum  crucible, 
care  being  taken  to  avoid  all  loss  by  dusting.  The  loss  of  weight  after  full  ignition  gives 
the  amount  of  chemically-combined  water  and  volatile  and  combustible  matter. 

(12)  The  ignited  soil  is  now  removed  to  a  porcelain  or  glass  beaker,  treated  with  four 
to  five  times  its  bulk  of  strong  nitric  acid,  digested  for  two  days,  evaporated  to  dryness 
first  over  the  water  bath  and  then  over  the  sand  bath,  moistened  with  nitric  acid,  heated 
and  treated  with  water.  After  standing  a  few  hours  on  the  water  bath  it  is  filtered  off 
from  the  insoluble  residue  and  the  filtrate  is  evaporated  to  a  very  small  bulk  (10  cc), 
and  treated  with  about  twice  its  bulk  of  the  usual  ammonium  molybdate  solution,  thus 
precipitating  the  phosphoric  acid.  After  standing  at  least  twelve  hours,  at  first  at  a 
temperature  of  about  50°  O,  it  is  filtered  off  and  washed  with  a  solution  of  ammonium 
nitrate  acidified  with  nitric  acid.  The  washed  precipitate  is  dissolved  on  the  filter  with 
dilute  ammonia  water.    After  washing  the  filter  carefully  the  ammoniacal  solution  is 


—  21  — 

treated  with  magnesia  mixture,  by  which  the  phosphoric  acid  is  precipitated.  After 
allowing  it  to  stand  twenty-four  hours  it  is  filtered  off,  washed  in  the  usual  way,  dried, 
ignited,  and  weighed  as  magnesium  pyrophosphate,  from  which  the  phosphoric  acid  is 
calculated.  The  per  cent  of  phosphoric  acid  found  is  to  be  subtracted  from  that  of  the 
alumina.  When  a  gelatinous  residue  remains  on  the  filter  after  dissolving  the  molybdo- 
phosphate  with  ammonia  it  may  consist  either  of  silica  not  rendered  fully  insoluble  in 
the  first  evaporation,  or,  more  rarely,  of  alumina  containing  phosphate.  It  should  be 
treated  with  strong  nitric  acid,  and  the  filtrate  with  ammonic  molybdate;  any  precipi- 
tate formed  is  of  course  added  to  the  main  quantity  before  precipitating  with  magnesia 
solution. 

HUMUS  DETERMINATION  IN  SOILS. 

The  estimation  of  "  humus"  by  combustion,  in  any  form,  of  the  total  organic  matter 
in  the  soil  gives  results  varying  according  to  the  season,  and  having  no  direct  relation 
to  the  active  humus  of  the  soil.  The  same  objection  lies  against  extraction  with  strong 
caustic  lye,  which  quickly  humifies  additional  organic  matter  present.  To  obtain  an 
estimate  of  the  humus  actually  active  in  plant  nutrition  through  nitrification,  we  must 
eliminate  the  unhumified  organic  matter.  The  best  mode  for  accomplishing  this,  thus 
far  known,  is : 

GRANDEATj'S    METHOD. 

About  10  grams  of  soil  is  weighed  off  into  a  prepared  filter.  The  soil  should  be 
covered  with  a  piece  of  paper  (a  filter)  so  as  to  prevent  it  from  packing  when  solvents 
are  poured  on  it.  It  is  now  treated  with  hydrochloric  acid  from  0.5  per  cent  to  1  per 
cent  strong  (25^  cc.  of  strong  acid  and  808  cc.  of  water)  to  dissolve  out  the  lime  and 
magnesia  which  prevent  the  humus  from  dissolving  in  the  ammonia.  Treat  with  the 
acid  until  there  is  no  reaction  for  lime ;  then  wash  out  the  acid  with  water  to  neutral 
reaction.  Dissolve  the  humus  with  weak  ammonia  water,  prepared  by  diluting  common 
saturated  ammonia  water  (178  cc.  ammonia  to  422  cc.  water).  Evaporate  the  humus 
solution  to  dryness  in  a  weighed  platinum  dish  at  100°  C;  weigh,  then  ignite;  the  loss 
of  weight  gives  the  weight  of  humus,  the  matiere  noire  of  Grandeau. 

The  examination  of  the  ash  of  this  humus,  which  contains  notable  amounts  of  phos- 
phoric acid,  potash,  lime,  and  magnesia,  does  not  appear  to  offer  sufficient  information 
to  justify  its  analysis  in  ordinary  cases. 

DETERMINATION  OP  NITROGEN  IN  SOILS. 

The  humus  determination  has  been  thought  to  indicate  approximately  the  store  of 
nitrogen  in  the  soil,  which  must  be  gradually  made  available  by  nitrification.  Ordina- 
rily (outside  of  the  arid  regions)  the  determination  of  ammonia  and  nitrates  present  in 
the  soil  is  of  little  interest  for  general  purposes,  since  these  factors  will  vary  with  the 
season  and  from  day  to  day.  Kedzie  (in  the  report  above  quoted)  proposes  to  estimate 
the  active  soil  nitrogen  (ammonia  plus  nitrates  and  nitrites)  by  treatment  of  the  whole 
soil  with  sodium  amalgam  and  distillation  with  lime.  The  objection  to  this  process  is 
that  the  formation  of  ammonia  by  the  reaction  of  the  alkali  and  lime  upon  the  humus 
amides  would  greatly  exaggerate  the  active  nitrogen  and  lead  to  a  serious  overestimate 
of  the  soil's  immediate  resources. 

The  usual  estimate  of  nitrogen  in  black  soil-humus  (Grandeau's  matiere  noire,  de- 
termined as  above)  is  from  5  to  6  per  cent  in  the  regions  of  summer  rains.  From  late 
determinations  it  would  seem  that  in  the  arid  regions  the  usually  small  amount  of  humus 
(often  less  than  0.20  per  cent)  is  materially  compensated  by  a  materially  higher  nitrogen 
percentage.  It  thus  becomes  necessary  to  determine  the  humus-nitrogen  directly  ;  and 
this  is  easily  done  by  substituting  in  the  Grandeau  process  of  humus-extraction,  potash 
or  soda  lye  for  ammonia  water,  and  determining  the  nitrogen  by  the  Kjeldahl  method 
in  trie  filtrate.  While  it  is  possible  that  the  ammonia  water  would  not  vitiate  the 
determination  of  nitrogen  in  the  case  of  neutral  or  calcareous  soils,  it  would  certainly 
do  so  in  the  case  of  those  having  an  acid  reaction. 

The  lye  used  should  have  the  strength  of  4  per  cent  in  the  case  of  potassic  hydrate, 
3  per  cent  in  that  of  sodic  hydrate.  The  black  humus  filtrate  or  an  aliquot  part  is 
placed  in  the  Kjeldahl  flask  with  concentrated  sulfuric  acid,  and  the  nitrogen  deter- 
mined in  the  usual  way. 


—  22  — 

To  this  method  the  objection  has  been  made  that  the  "humus"  extracted  by  fixed 
alkalies  is  not  necessarily  the  same  as  that  dissolved  by  ammonia.  This  objection  may 
be  obviated  by  extracting  two  separate  portions  (of  10  grams)  of  the  soil  with  ammonia, 
as  above,  and  using  the  one  for  the  determination  of  total  humus;  while  the  other' 
after  evaporation  to  small  volume,  is  mixed  with  about  5  per  cent  of  magnesic  oxid, 
which  in  boiling  eliminates  all  the  ammonia  that  has  been  taken  up  from  the  ammoniacal 
solvent;  after  which  the  nitrogen  in  the  residue  is  determined  by  the  usual  Kjeldahl 
method.  The  results  obtained  by  these  two  methods,  however,  usually  agree  very 
closely. 

For  the  determination  of  nitrates  in  the  soil  it  is,  of  course,  usually  necessary  to  use 
large  amounts  of  material,  say  not  less  than  50  grams  and,  according  to  circumstances, 
five  or  more  times  that  amount.  In  the  evaporated  solution  the  nitric  acid  is  best 
determined  by  the  reduction  method,  as  ammonia. 

Usually  the  soil-filtrate  is  clear  and  contains  no  appreciable  amount  of  organic 
matter  that  would  interfere  with  the  determination;  yet  in  the  case  of  alkaline  soils 
(impregnated  with  carbonate  of  soda)  a  very  dark-colored  solution  may  be  obtained. 
In  that  case  the  soil  may  advantageously  be  mixed  with  a  few  per  cent  of  powdered 
gypsum  before  leaching;  or  the  gypsum  may  be  used  in  the  filtrate  to  discolor  it  by  the 
decomposition  of  sodic  carbonate  and  the  precipitation  of  calcic  humate.  The  evapo- 
rated filtrate  can  then  be  used  for  the  nitrate  determination  by  either  the  Kjeldahl, 
Sprengel,  or  the  colorimetric  method,  which  will,  of  course,  include  such  portions  of 
the  ammoniacal  salts  as  may  have  been  leached  out. 

For  the  separate  determination  of  these  and  of  the  occluded  ammonia,  when  desired, 
it  is  probably  best  to  mix  the  wetted  soil  intimately  with  about  10  per  cent  of  magnesic 
oxid  and  distill  off  into  titrated  chlorhydric  acid.  For  general  purposes,  however,  this 
determination  is  usually  of  little  interest. 

DETERMINATION  OF  "PROBABLY  AVAILABLE  PLANT  FOOD." 
(Dyer's  Method.) 

The  methods  of  chemical  soil  analysis  discussed  in  the  preceding  pages  are  intended 
to  show  the  entire  amount  of  mineral  plant  food  likely  to  become  available  within  the 
time  interesting  to  the  present  and  several  succeeding  generations,  with  a  view  to  per- 
manent investments.  In  the  case  of  virgin  soils  the  adequate  availability  of  these 
ingredients,  and  the  consequent  duration  of  productiveness,  may  usually  be  assumed  to 
be  in  more  or  less  direct  proportion  to  the  total  amounts  found.  But  in  the  case  of  soils 
long  cultivated,  it  is  extremely  desirable  to  ascertain  somewhat  definitely  the  present 
needs  of  the  soil,  so  as  not  to  waste  money  on  the  purchase  of  unnecessary  fertilizers. 
Numerous  methods  for  this  purpose  have  been  suggested,  from  the  extraction  with 
large  amounts  of  pure  water  to  that  with  dilute  chlorhydric  acid,  and  various  salts.  Of 
all  these  methods  none  seems  to  accord  so  nearly  with  the  results  of  practical  culture  as 
the  extraction  of  the  soil  with  a  2  per  cent  solution  of  citric  acid,  originally  suggested 
by  Maerker,  and  later  more  definitely  developed  by  Dr.  Dyer,  whose  name  the  method 
usually  bears.  Dyer's  method,  somewhat  modified  to  conform  to  the  conditions  of  the 
arid  region,  is  as  follows: 

Place  in  a  flask,  or  bottle,  100  grams  of  air-dried  soil  and  600  cc.  of  distilled  water  con- 
taining 12  grams  of  pure  citric  acid.  (Whenever  the  soil  contains  carbonates,  a  proper 
allowance  must  be  made  for  them  by  a  corresponding  increase  in  the  dose  of  citric  acid.) 
The  soil  is  left  at  room  temperature  in  contact  with  the  2  per  cent  sc  lution  of  citric  acid 
for  twenty-four  hours,  with  frequent  thorough  shaking.  At  the  end  of  the  digestion  the 
solution  is  filtered,  and  divided  into  three  parts— one  for  the  potash,  and  one  for  the 
phosphoric  acid  determination,  the  third  as  a  reserve.  Evaporate  each  to  dryness, 
ignite,  and  determine  the  potash  and  phosphoric  acid  according  to  the  methods  given 
above  for  the  general  analysis  of  the  soil. 

PRESENTATION  AND  INTERPRETATION  OF  RESULTS. 

It  is  strenuously  suggested  that  in  the  presentation  of  the  results  of  a  soil  analysis 
the  order  of  the  electrolytic  series  be  observed,  as  in  the  schedule  annexed,  so  as  to 


—  23  — 

facilitate  comparisons  which  are  rendered  unnecessarily  troublesome  by  differences  in 
arrangement.  The  insoluble  residue  is  best  placed  at  the  head  of  the  column.'as  it 
indicates  at  a  glance,  approximately,  the  general  character  of  the  soil  as  sandy,  loamy, 
or  clayey. 


Coarse  materials  >>0.50mm 
Fine  earth 


100.00 
Chemical  Analysis  of  Fine  Earth. 

Insoluble  matter _ 

Soluble  silica - 

Potash  (K20) 

Soda(Na20)  

Lime(CaO) 

Magnesia  (MgO) 

Br.  ox.  of  Manganese  (Mn304) 

Peroxid  of  Iron  (Fe2(J3) 

Alumina  (A1203) 

Phosphoric  acid  (P205)  ...  .. 

Sulfuric  acid  (S03) _ 

Carbonic  acid  (C02) 

Water  and  organic  matter 

Total 


Water-soluble  matter,  per  cent. 
Chlorin,  per  cent 


Humus 

Ash 

"        Nitrogen,  per  cent  in  Humus 
"  "  per  cent  in  Soil 


Available  Potash j  citric  acid 

Available  Phosphoric  Acid  ]    method 

Hygroscopic  moisture,  absorbed  at °  C. 


Water  capacity :  By  Volume.  By  Weight. 

Maximum _ _ 

Minimum 


For  suggestions  concerning  the  interpretation  of  analyses  made  according  to  the 
above  methods,  see  "Report  on  the  Experiment  Station  of  the  University  of  California," 
1890,  pages  151  to  172. 


